View Full Version : How Do I Verify Oil Pressure?
DennisG01
02-26-2008, 08:20
Is there an easy way to verify what my oil pressure gauge is reading? I installed a remote oil pressure sensor, wired up to a light on my dash. The remote sensor is *supposed* to be calibrated at 20psi. However, according to my stock, dash gauge, the extra light I installed comes on once the pressure drops to about 30-32 psi. I'd like to figure out which is correct - the stock, dash gauge or the new, remote sensor.
This picture shows the oil pressure sensor (blue shrink wrap):
http://www.thedieselpageforums.com/photopost/data/519/medium/DSC01123.JPG
Ahhhh one of my personal questionable and still not satisfied understanding of oil flow specifics.
How long have you been running the warning light and has it worked as intended before?
You could rig up a cheap mechanical guage to that port and see what it sees for pressure. That would diagnose the warning light function. Depending on speed of switch see below.
Find out specifics for the switch function does warning light come on at instant of 19.99 psi and or 2-3 seconds of <20 psi and it turns off with 2-3 seconds of >20 psi etc that might make a difference. Are you measuring the pressure pre or post filter media? That could dampen pressure spikes of oil flow especially as media plugs more. My guess is the complex flow path and bypass valves are messin with the light. If you measure downstream of filter and bypass's in an oil gallery I bet your oil pressure is close to what your dash gauge reads.
I personally don't believe 100% of the oil goes through the filter or cooler for that matter in normal driving 100% of the time. But I won't tangent for now until I understand more of your problem.
Also explain how its worked so far.
I interpret light goes out when dash gauge reads above 32 psi. Is that cold and you are reading what about 60 psi idling then warm it dips to 30 ish psi idling and up to 50-60ish at 2000 rpm the light goes on and off depending on what???
Couple of things to consider:
The oil pressure depends in part on where you measure it. Don't expect 2 sensors at different places in the engine to read the same.
The switch turns on and off in response to changing pressure. The gauge may respond more or less slowly to the same changes.
10 psi at idle is more than enough. 45 psi is more than enough for all operations.
What size hoses are you running to the filter?
One thing I hesitate to question is how does that pressure switch work? Because I don't know exactly. Is it one wire one terminal or is it 2 hard to tell from pic looks like one wire and its suppose to ground to achieve ok signal. But looks like you have rubber for shock absorbtion in mounting filter head and again inbetween mount fixture and truck body so can it achieve good ground or is it open without vibrations or intermittents ???
DennisG01
02-26-2008, 18:54
One thing I hesitate to question is how does that pressure switch work? Because I don't know exactly. Is it one wire one terminal or is it 2 hard to tell from pic looks like one wire and its suppose to ground to achieve ok signal. But looks like you have rubber for shock absorbtion in mounting filter head and again inbetween mount fixture and truck body so can it achieve good ground or is it open without vibrations or intermittents ???
Well, that's a good point - and a mighty keen eye, as well! Yes, it is a one-wire hookup. Yes, there is a rubber gasket between the mounts for vibration dampening. However, I think it ends up grounding through the SS lines. Now, I must say that this was not my intention. When I put this together I was well aware of how it's supposed to ground, but in the process I simply overlooked that step. Looks like I got lucky, 'cause the light on the dash seems to be working quite well - never any "intermittent" on time to indicate bad grounding. At night, it's awful bright! By the way, with the install of the new engine I cleaned all ground mounting points, replaced all ground straps with new/larger ones, and replaced all battery cables with 1-gauge. I even replaced the + cable that goes from the driver's battery to the main fuse box with a new cable about 2 sizes larger.
OK, here's some more detail. I used -8 hoses as I was concerned about -10 possibly causing a slight drop in oil pressure. To keep things simple, I'll refer to things as "DG" (the PSI reading at the "Dash Gauge") or "RL" ("Red Light" on the dash, wired to the remote sensor).
I just recently hooked this up with the install of the new engine (less than a week ago) - although I have been using the remote oil filter for some time, just not the oil pressure sensor. So, I don't have a comparison. What I can say, is the DG seems to operate the same as it did before. Meaning, how quickly the needle reacts/the extent of the high and low swings/what the PSI reads when the engine is cold or warm/how the needle reacts to RPM's. So it seems as the DG is operating exactly the same as before.
At cold idle, the DG reads close to 60. At warm idle, it reads about 25. So once the engine warms up, then the RL will come on at idle. After the engine is warm, if I increase the RPM's to about 900 the RL will go out. This corresponds to about 32 PSI on the DG. The RL will come on and off very quickly - faster than the needle swings.
By the way, the pressure sensor is actually located in an "IN" port on the filter mount as I'm intending the other "OUT" port for a bypass filter. However, my thought was there should still be the same pressure at the "IN" port since fluid takes the path of least resistance. I discussed this with a guy at my local injection shop and we both agreed. Does this make sense or am I missing something?
I guess what I need to do to really know for sure is hook up a mechanical gauge (as suggested above) where the sensor is? Is there a better place to hook up a gauge?
Sorry for the long reply!:rolleyes:
This is the filter mount: http://static.summitracing.com/global/images/prod/large/prm-1793_w.jpg
The -8 lines should be fine. A -10 should not drop psi as it's just a vessel carrying oil to the point of leak which is the bearings...
I am very interested in the outcome of this. I THINK the oil filter bypass valve is the reason the light comes on and its normal. Probably a bit less oil goes through your remote mount but its still operating as intended and ok.
I think for the scope of engine oil passages pressure should still be higher upstream than down stream. As flow will take path of least resistance.
OK JMHO lots of thought and some looking into.... I think the oil filter bypass valve works 2 ways:
1. As a direct path pressure relief bypass. (At low flow and/or lower pressure)
2. As check valve with a differential pressure release across filter media. (at higher flow and/or higher backside pressures).
OR it provides for a minium of 17-19 psi differential to the filter media not sure exactly what is going on here. Its a parallel path of oil flow for sure with a checkvalve and restriction.....
Looking at it its a built like a check valve and a direct pressure release with a spring. It has differing piston face sizes exposed to the check valve sealing piston/operation. So that on initial exposure to flow it opens at about 17-19 psi but once flow stabilizes it will shut and stay shut until some larger differential and or check valve operation opens it due to plugged media. I can't remember I tried back of envelope calculation and wasn't sure of outcome on differential pressure release opening (I think it varies according to backpressure somehow and or flow properties). But to me it has 2 modes of bypass direct and differential checkvalve of sometype. In actual operation it will open at plugged media and it also won't restrict oil flow to main galleries at low oil flow. I think its a simple neat little mechanism operation hard to explain with text.
The oil pump pumps volume of oil depending on rpm. Oil pressure will rise as a restriction to oil flow downstream.
At idle the OP supplies enough volume of oil to build approx 20-35 psi at the oil gallery warm due to the size of bearing clearances and remainder of oil path vs the volume of oil supplied at RPM. --- Increase the RPM ( OP flow volume) and oil pressure goes up as restriction to flow downstream. But the oil gallery doesn't care where oil came from.
So here is what flow does oil pump is pumping and it bypasses filter because not enough backside pressure on bypass valve to hold it shut but the orifice size in bypass is small it still restricts flow so some oil will go to filter too. Enough oil volume is pumping to build 32 psi at gallery but filter head see less than 20 psi because not sure but maybe 10-19 psi of oil pressure flow is bypassing with the valve.
Now increase rpm more oil flow from the pump the orifice in the bypass valve is a restriction so pressure increases on flow to the filter head at that point. Now the filter head sees more than 20 psi and light goes out. Oil gallery sees more flow from bypass and filter so pressure reads >32 psi because downstream restrict stays the same.
Cold the orifice size in bypass valve is such that filter head sees more than 20 psi light is off. As it warms more oil can go through bypass valve oil orifice and filter head sees less than 20 psi. Cold the down stream of oil gallery path sizes/clearances build 60 psi of oil pressure.
I think your warning light is a safety and if you use a lower pressure switch say 10psi maybe 15 psi it will work as intended and you'll know a tinsy bit faster if you loose oil flow due to cooler or remote line to filter failure. You'll still have to watch oil pressure guage for safety but warning light will be a earlies catastrophic failure alert. Or put warning light at 20 psi in main oil gallery and that will work too until engine is old and won't maintain 20 psi oil pressure
hmmm
AND or also might alert you to bad DG or hot oil that drops below 20 psi.
I still get a bit confussed on actual operation of this bypass valve. It may open if greater than 19 psi differential is on filter media and provide some lesser retricted flow to bearings at low volume flow say at idling 32 psi dash guage. But due to its orifice size will always provide some restriction to flow bypass and push oil through filter too. So in which case why the spring is it just a checkvalve so oil won't drain back out of oil galleries?
I have read marine gassers up the bypass spring pressure when running remote mount oil filters and wonder why and if its important to do so. I have seen oil bypass plugs too and wonder if they are dangerous for daily drivers as cold start up would see some reduced flow to bearings.
Comments welcome.
DennisG01
02-27-2008, 09:20
OK, I think I'm pickin' up what you're puttin' down. If I'm understanding you correctly (and JohnC.), both the remote sensor and the DG are probably correct. It's just that the oil pressure is actually different at the remote sensor and wherever the sensor is for the DG (by the way, where is it?).
I certainly would prefer that this red light doesn't come on all of the time. However, I would also prefer to keep the 20psi sensor instead of dropping down to 10 or 15 - simply as it would give me more "heads up" time.
Where is this "oil gallery" that you speak of?
The oil gallery is up in the valley of the motor feeds the cam bearings and or then mains etc There are 2 one for each side of V. The dash guage sensor is ported to one of the galleries (think its the left one) at the upper or rear of engine the poplular oil pressure switch I believe. I think Jim's pic of the AMG/GEP engine block differences points the port out.
I don't think the oil filter bypass valve should be bypassing under normal circumstances. If it is, unfiltered oil is getting to the engine.
Put a mechanical gauge on both ports (one at a time) and get readings under comparable RPM and oil temperature and compare them. The accuracy of the gauge is not important; you're just trying to quantify the difference between the 2 positions. The panel gauge is nortoriously inaccurate; better for trend analysis than absolute readings.
Unless they have come up with a new numbering system, a -10 hose is bigger than a -8 and would have less effect on pressure, not more, right?
Having 2 oil pressure sensors is like having 2 watches. You'll never know for sure what time it is...
Less than 20 psi at hot idle is not necessarily something to worry about.
DennisG01
02-27-2008, 11:18
Unless they have come up with a new numbering system, a -10 hose is bigger than a -8 and would have less effect on pressure, not more, right?
Well, my thinking is that the larger the vessel (hose), the lower the pressure will drop. Same amount of fluid pumped through a larger tube will decrease pressure in the tube. -8 and -10 are awful close, so maybe the difference is negligible. As stated above, maybe it's not so much the size of the hose and more what's at the end of the hose that controls the pressure (unless we start exagerating the hose size).
I don't disagree with that JohnC but stand behind all that I wrote. I have read lately that Ford's oil pressure gauges are "fake" and if minium oil pressure is measured the guage needle sits in middle. I thought GM's gauges were real psi measurement and not that fake and is in the ball park of accurate. Hopefully at least within 10-12 psi but have also always wondered about the specs being so low in relation to gauge.
Would you or anyone care to comment on just how the bypass valve works? I would like to understand initial and steady state operation of flow.
Not having 100% of oil filtered 100% of the time is more the reality from my research. Its the constant loop and refiltering that keeps the oil ok. Oil filters are not absolute filtration but multipass effeiciency is pretty good.
I asked Dr Lee this very question several years back, and, unless I missunderstood his answer, he said that the bypass should not open under normal circumstances.
The purpose of the bypass is to prevent oil starvation should the filter become plugged, not to dampen momentary pressure variations. Seems to me the proper choice of valve would take normal pressure variations into account. Oil picks up its debris on the way back to the filter, not between the filter and it's appointed rounds (barring catastrophic failure), so there is no guaranty that oil from the sump doesn't have something damaging in it no matter how often it has been through the filter in the past. Seems like a bad bet to me!
Dennis - I think the pressure-velocity relationship is inconsequential at these flow rates. Regardless, any pressure change in the lines is nullified once the oil reaches the filter. I'd go for the larger lines to cut down on frictional losses. Pressure lost due to flow changes can be recovered. Frictional losses are forever...
The gauge on my '95 was not fake, I just don't think it was intended to be accurate. Besides, a 10 psi error is more than enough to account for the differences being discussed here.
True and I need to rethink it AGAIN because I am not sure flow would not reverse some if gallery is at 32 and filter inlet was at 20 as oil pressure as in general flow travels from hi to low.
More thoughts to come the oil bypass is killing me.
Oil contamination is cumulative and continuous filtration removes the big stuff. You can run an engine on unfiltered oil ok for a while you can do partial filtration per loop and circulation and run a really long time (idea behind oilguard type systems). I think the amount of oil that actually gets filter is a bit of an unknown when running a remote mount filter with bypass not adjusted. Why have different bypass pressures?
I can see the oil pressure being slightly higher in the oil gallery than the filter inlet due to the bypass but not excessively.
Other ideas on how it works?
BTW, good catch on the missing ground wire!
The bypass valve opens in response to a differential pressure between the filter inlet and outlet. If the valve is open, then, by definition, the pressure at the filter outlet must be lower than the inlet. The outlet is plumbed directly to the gallery in question. No way the bypass can raise the gallery pressure above the pressure at the filter outlet. It's the salamander eating its tail...
I might buy it if the bypass emptied into the opposite end of the gallery, but it doesn't. It empties right at the filter outlet, or, in this case, where the return hose enters the engine.
Ok ya'll probably think I am nuts but I still just question this bypass valve and remote mount filters.
Before I ramble on too much can someone tell me some fairly accurate oil pressure readings at the oil gallery in a normal and or realitively fresh engine? Is dash gauge within 2,6 or 10 psi of accuracy?
I keep running around in circles. If dash guage reads 30-31 psi and light sensor sees less than 20 psi in a perfect world no friction loss or drop in pressure across filter media etc There is an error of 10-11 psi. But there has to be some pressure drop across filter media, hose lenght, and funky orifices of fittings and path ways etc plus sensor height differences so pressure back at filter head should be higher by at least 2-4 psi??? Therefore you really have to account for about 12 -15 psi gauge inaccuracy???? Is it that bad?
Conversely assume pressure gauge is only accurate to within 10-11 psi thats about 33% error but ok assuming thats the case: the oil gallery is really only about 19-20 psi and assume there is only about 1-1.5 psi drop across across filter media and 2? ft of hose, a couple of fittings and nasty "K" factors for flow through bypass mount and adapters height etc so pressure at light sensor would be 20-22 psi and light should be off ????
I am just somewhat surprised at the amount of error in dash guage. (I have read its not real accurate but thought it might be somewhat close). My second arguement still exceeds specs more than double just seems low (from seeing 30-60 psi on dash guages) and/or points to a really inaccurate dash guage??? Again just somewhat surprised.
DennisG01
02-29-2008, 11:43
in a perfect world no friction loss or drop in pressure across filter media
However, keep in mind that in my case, the remote pressure sensor is plumbed into the extra IN port on the remote filter mount. So filter media friction should not be coming into play. I know, small point, but just to keep things straight...:p
Also, I checked out the pics (the one you linked to, above) about where the oil gallery/pressure port is. Then I looked at some of the pics that Ron Schoolcraft sent me of my engine during the build. Unless I'm mistaken, I think only see one port in the valley. I'll post the pic later and maybe someone can verify if I'm looking at the right thing.
Thats my point if warning light is on in side of filter head (either end of filter head) then the dash guage would be on other side "down stream". Which is why I added a guestimate of pressure drop across filter media comparing warning light to dash guage. But only 1/2 hose lenght for warning light and DG comparison. Note the bypass valve would see entire loop whereas normally it only sees pressure differential across filter media.
Actually, I THINK? I am pretty low on my pressure drop guestimates just to see what ya'll think.
I found a website that let me plug in and calculated some theoretical pressure drops and the bypass valve opening may not not really be that big of stretch. But it doesn't make sense if I am really off on guestimates of pressures and flow is why I did not post link.
ronniejoe
02-29-2008, 13:59
Dennis,
The older engines only had one pressure port in the galley at the top of the engine. It was located at the back of the block, behind the head. The oil pressure switch was mounted into a funky looking elbow to clear the firewall. Later engines also had a port in the valley of the engine under the intake. Your engine has a plug in the rear port and your sending unit is in the port in the valley. That's where the factory put it on later engines. You can't see the rear port very well in the pictures I sent you because there is an electrical connector laying on top of the rear port covering it up. If you look closely at photo IM002266, you can barely make out the plug in the port behind the connector.
Who says either one is accurate? Quit speculating and get one gauge and measure the pressure in both places under the same circumstances.
DennisG01
02-29-2008, 17:03
Dennis,
The older engines only had one pressure port in the galley at the top of the engine. It was located at the back of the block, behind the head. The oil pressure switch was mounted into a funky looking elbow to clear the firewall. Later engines also had a port in the valley of the engine under the intake. Your engine has a plug in the rear port and your sending unit is in the port in the valley. That's where the factory put it on later engines. You can't see the rear port very well in the pictures I sent you because there is an electrical connector laying on top of the rear port covering it up. If you look closely at photo IM002266, you can barely make out the plug in the port behind the connector.
Is this the unused/plugged port? (see big pic, then zoomed-in pic)
http://www.thedieselpageforums.com/photopost/data/519/medium/IM002266.jpg
http://www.thedieselpageforums.com/photopost/data/519/IM002266_2.jpg
Is this where the sender goes?
http://www.thedieselpageforums.com/photopost/data/519/medium/IM002255.jpg
http://www.thedieselpageforums.com/photopost/data/519/IM002255_2.jpg
The garage that did my install has a pressure gauge. Hooking in to my remote oil lines will be simple. From these pics (it's dark outside, right now) it looks as if I might be able to get to that unused port by moving the glow plug relay (if I am correctly identifying the locations in these pics)?
Yes, I believe either of those 2 ports should equal the dash gauge reading.
ronniejoe
02-29-2008, 18:58
http://www.thedieselpageforums.com/photopost/data/500/medium/IM001165.JPG
This photo shows both locations clearly. The stock oil switch is in the aft location in the elbow that I described earlier. A second switch is in the newer location in the valley of the engine. This switch is part of Kennedy's lift pump harness kit.
The pictures that you posted earlier show you are looking at the forward port. The machine shop had installed a plug in that port. In the first picture that you posted, you can barely see the aft port with plug in it under the electrical connecter hanging down. The zoomed image of this photo shows the sender in the forward port.
The second picture and its zoomed image show the forward port with the machine shop installed plug. This plug was later removed and your sender installed.
DennisG01
03-11-2008, 05:33
OK, I don't have anything new to add, yet. But there is a plan! Between two jobs, it's just been so hectic lately I haven't had time to get the proper fittings I need to T into the lines at the stock location.
I found the unused plug on the back of the driver's head, but, just about impossible for me to use that - maybe if I removed the manifold and attacked from underneath. Even if it's possible, it's not very feasible: remove the manifold, take out the plug, install a gauge... all while the engine is hot? I don't have a gauge, so this needs to be done at a garage and I want to be there when this is happening (which is fine with the garage), but it will end up taking too much time.
So, in talking with Ron, he suggested using the oil pressure line that goes to the turbo. Much easier!!! Thanks, Ron! I'm going to make it easy and use the end that is at the turbo. Bad thing is this brings in another variable (possible resistance in that line), but oh well.
I called a dealer in hopes of finding out what size that ?NPT? fitting is on the turbo, but he couldn't find a spec. So I'll just take a wrench with me and go to a supply store and try some fittings out while I'm there.
??? Does anyone happen to know what size that fitting is? It'll save me a little time if you do, but not that big of deal - don't go to any hassle to find out!
Also, just on a side note - is there anything special to an oil pressure gauge, or can any pressure gauge work? What could I expect to pay for a good (but not professional grade) kit?
DennisG01
03-12-2008, 05:37
If you have experience with oil pressure checkers, what do you think of this? Look at "KD 3343".
I'm thinking it's going to cost me about $30 for the mechanic's time to help me check the oil pressure, this tool is only $20 more. But, I believe in the "buy it right the first time" philosophy and if this tool is junk, I'll forget about it.
http://www.mytoolstore.com/kd/kdengi12.html
So for $50 you get a kit to verify oil pressure. I don't know. I did not see a reference to its accuracy I don't see where it is any more or less accurate than any other automotive mount oil pressure guage.
I googled a bit but did not see what I would want if it were me. I thought Autometer or some guage mfg did advertise a % accuracy for some series but can't find it now?
I would say why not buy a good quality regular guage that you can mount permanently either under hood or down low under dash and just spot check it for comparison to keep dash guage reference honest.
I'll try and look some more for accuracy claims.
Maybe I missed something here????????//
If you are worried about the accuracy of your dash gauge this is an easy thing to fix.
Install a T fitting into the oil passage at the front or the back of the block and put in a direct reading gauge.
The dash gauges on these trucks, no matter if its the Oil pressure or the coolant temp or volt meter are a guess at best.
My trucks gauges will vary some and its due to system voltatge and several other factors.
If I hit the door lock button and hold it the gauges will move (All of them)
I cant find anything in the way of wiring issues so its probably a voltage regulator thing on the panel board ?????/
Install your oil pressure gauge and be happy with what it says.
The direct reading gauges you get from most of the major companies are going to be within a pound or two +/-
The 6.5 should see 40 or so hot running down the road and idle at around 20 give or take.
This is with 15-40 diesel rated oil
Best
Robyn
I couldn't find much literature on gauge accuracy so I emailed Sunpro. No real reason I picked Sunpro they just had an inexpensive mechanical gauge. They responded with this....
" The CP8216 is tested to be within +/- 5 psi @ 40 psi of applied pressure, which can also be stated "within one division" or "within 5 %". This accuracy should be consistent across the dial. "
---------------
Probably fairly standard like Robyn said unless you want to buy lab instrument grade stuff.?
I have heard people say that mechanical gauges were a little more accurate. I don't know if its necessarily true.
..within +/- 5 psi @ 40 psi of applied pressure, which can also be stated ... "within 5 %"
Must be "new math..."
;)
Precision is more important than accuracy. Use the same gauge in both ports and get and idea of the magnitude of the difference between them. The absolute value is not that important.
DennisG01
03-13-2008, 14:54
Thanks, everybody, for the input. Based on what you guys are saying, I think I'll forgo that kit that I linked to. Besides, I just noticed it's a 0 - 300psi dial face. Might be kinda hard to see what it's reading.
I just talked to one of the mechanics at my second job (marina) and he is going to let me borrow his Stewart-Warner mechanical gauge. I'll post back when I have the numbers...
Must be "new math..."
;)
Precision is more important than accuracy. Use the same gauge in both ports and get and idea of the magnitude of the difference between them. The absolute value is not that important.
Yeah John out of context it sounds bad. In fairness to Sunpro tech support here is what I had asked them...
-------
my email:
"I am looking at verifying my OEM dash oil pressure gauge in my diesel pickup truck (15w-40 oil if it matters). I have been told the dash guage is not very accurate.
What is the accuracy of your oil pressure gauges?
CP8216 is your mechanical oil pressure gauge 0-100 psi. Will it read within 2% accuracy? And explain accuracy please I think most claim its within x% of full sweep so at 5% of 100 psi it is what +/- 5 psi accuracy at any measurement or is it a % of the reading. For instance at 50 psi is it within 5% at that reading or +/- 2.5 psi or is still at +/- 5 psi ???
Sincerely,
Hubert
Pendleton, SC"
------------
I have forgotten a lot of verbage of gauge R&R, accuracy, and precision. I am skeptical it really maintains uniform accuracy over the full range because its really a spring type mechanical device. I think usually you say its a % of full sweep value hence the 5 psi ~ 5% above. But I wonder if its closer at the calibrated 40 psi then tapers off at either end of range. Or if it can be stated a % at reading.
I'm still not sure exactly what you're trying to accomplish. I first thought you were trying to explain the difference between the dash gauge and the pressure switch. Now it sounds like you are trying to figure out exactly how much oil pressure you have.
I submit this is not important, as long as you have more than enough, which you must have given the engine has not come apart. Once this is accepted, any gauge or warning light you have is used for trend monitoring. For this purpose, precision is desireable over accuracy. As long as the readings are consistent from day today for a given set of conditions, nothing has changed and you still have "more than enough".
I absolute terms, there are too many variables to say whether a particular reading is acceptable or not.
DennisG01
03-14-2008, 12:32
Ultimately, I just want this bright red light to go off under normal circumstances. In the end, I may just put in a lower PSI sensor. However, if I can keep the 20 PSI, I would prefer to do that as it may give me just a little more time in the event of a failure.
Along the way, it would be nice to know how close to accurate the dash gauge is and how much of a pressure difference there is between the stock pressure sensor and a one mounted at a different location. True, there are some variables here that don't allow for an exact comparison, but a general consensus would be interesting. And, yes, I do realize that the actual PSI number is not as important as making sure there is enough flow - flow being the most important thing, not necessarily how much pressure it's under. So, yes, I do agree with you that the dash gauge is best used for "trends".
DennisG01
03-16-2008, 11:52
OK, here's the scoop. I borrowed my friend's mechanical gauge (as mentioned above) and I took readings at the remote filter mount and on top of the turbo where the pressure line attaches. Again, this is probably not the best place, but I think it does give a good comparison. This was done with 15/40 oil and at normal operating temp. MG = Mechanical Gauge PSI DG = Dash Gauge PSI
At Remote Filter Mount:
RPM MG DG
Idle 13 35
1000 17 38
1300 19 42
At Turbo:
RPM MG DG
Idle 13 35
1000 16 38
1300 19 42
I also moved the remote pressure sensor on top of the turbo. It goes on/off just the same as before. I guess I'll try a lower PSI pressure sensor.
DmaxMaverick
03-16-2008, 12:33
Now that you have a baseline, install the MG into the SAME HOLE as the OEM pressure sender. The OEM gages aren't known to be accurate, but it's hard to believe it's that far off. If your MG indicates the DG is off by the same amount, I'd suspect a bad sender, or a resistor somewhere in the circuit that's gone south. The locations you are testing now will be misleading. They will not indicate the actual regulated pressure the oil pump is putting out.
Also, run it up to 2000 RPM. The numbers from the mechanical gauge seem low, although it does seem to be consistent with the switch. If you don't get up to about 40 psi at 2000 I'd be concerned...
Maybe the pressure relief spring is broken...
DmaxMaverick
03-16-2008, 13:02
I agree. But the DG should not be indicating that high, if it is in fact remotely close. If the relief spring is broken, the DG should not indicate such a high pressure in any case. I too would be concerned if the pressure(s) doesn't indicate higher, even at 1000 RPM's. You need to see the the actual (or as close as possible) pressure at the bearings. The main gallery (where the OEM sender should be getting the input) should indicate a pressure closer to that delivered to the bearings and lifters. If your pressure is in fact that low, you have issues that need to be addressed to keep a healthy engine.
DennisG01
03-16-2008, 15:17
At 2,000 RPM's, the MG (at turbo) reads 32psi, while the DG reads 42psi.
My DG readings seem to be inline with what it was before the new engine and also with what I remember reading about here on the Page in regards to other member's trucks and their readings - of course this is if "IIRC" ;).
Also, correct me if I'm wrong, but isn't the GM spec, at idle, for minimum PSI about 10psi?
I would like to get a reading at the stock location for the pressure sender, but it looks to be too much of a hassle for my purposes.
I am surprised at the readings. Its just not intuitive to me that the turbo location would have the same psi reading as filter head so far down stream and across filter media and all the loss of oil flow through various other paths. But pressure isn't everything. Flow is still unkown. All we really know is the orifices and path sizes are at least balanced well enough to still maintain pressure at turbo feed for its gpm flowrate.
I have to go back and relearn why the Bernoulli equation breaks down so and yields such poor estimates of pressure drop. I think its the size of the path and direction changes and diameter changes along the way that I am not accounting for.
Anyone want to say that and or this better. I think it relates to flow will always take the path of least resistance. Resistance is measured by psi so psi is the same for the system because of conservation of mass if pressure were lower somewhere more mass would flow that direction until it is restricted enough to empede flow. So as long as your feed flowrate exceeds all your exits by an appreciable amount it all equals out to flowrate follows path of least restriction. Flow rate will be different according to bearing clearances and path diameters but pressure remains the same???.
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I thought GM spec was 10 psi per 1000 rpm.
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I think if you measured say at remote mount line leaving the block and the remote mount line coming back to the block you might see a pressure drop due to friction but once you go down stream and are necked back down pressure increases again. And like I said above flowrate of oil pump still exceeds all the "exits" of the path so oil pressure is relatively the same measured for "the engine" but flowrate volume is considerably different.
I think the velocity is relatively low in this system so the Bernoulli effect is minimal. The gallery size is large relative to the "leaks" so the system looks more like a hydraulic cylinder that a flow system. In a hydraulic cylinder, pressure is evenly distributed over the entire surface, so the pressure at the turbo end would be the same as the pressure at the pump outlet. Any pressure drops are proportional to flow rates; slow flow == minimal pressure differences.
The 10 psi/1000 rpm is a generally accepted guideline, not GM and not a limit. I'm sure GM has a published limit, in fact I seem to recal seeing it somewhere in the service manual, but the "for public consumption" limit is "not in the red". I myself would be a little leary of pulling a trailer at 65 mph with oil pressure just a hair above the red...
I looked it up for reference my Helm Manual for my '97.... (pg 6A-258 Engine Mechanical Specifications).
oil pressure - hot
10 psi @ idle
40-45 psi @ 2000 rpm
69 Kpa @ idle
275-310 Kpa @2000 rpm
Great now this is clear as mud.
Driving last evening I looked and yep my dash gauge reads 42 psi @2000 rpm hot according to spec. Which I think is pretty normal I think. How many have verified actual oil pressure? I wonder if Helm manual spec is the dash gauge number or an actual independant measurement????
Looking at the oil path diagram it looks like the right oil gallery is fed via the back cam bearing. And the turbo feed is at the front end of the gallery. The left oil gallery is fed from either the oil filter or the bypasses. The left gallery feeds all the other cam bearings and then flow down to crank etc or up the lifters etc. So I can still wonder if there is some loss of flow affecting the measurements. There is a note of a cup plug with 0.06" hole at the filter base item 7 in my helm book diagram. Not sure what that does. Anybody know?
John brings up a good point but if you guestimate 1-3 gpm flowrate. Which I think is in the ballpark??? Velocity of oil through a 1/2" diameter hose would be roughly 1.6-5 ft/sec (unless I had a math error; very possible) which is not all that slow of flow???. I still wonder if high viscosity of oil doesn't affect things.
I just can't understand/explain the left oil gallery being at a significantly higher psi than filter head on inlet side.
Dennis do you have routing of remote lines crossed? I think at engine base OUT goes to filter head IN then filter head OUT goes to engine base IN right?
Any other thoughts? Just bad oil pump, poor dash gauge, and/or loose clearances?
ronniejoe
03-18-2008, 06:47
The clearances are dead on the nominal and I have photographic evidence to document the assertion. The pump is a brand new Melling unit. There is nothing wrong with the engine. This is simply a measurement accuracy issue.
I was the one who suggested checking pressure at the turbo feed. I didn't expect much drop from the core where pressure is measured for the gage. Maybe there is more than I thought. At this point, to put all the guessing and all the speculation about a "bad engine" to bed, you should remove the plug at the back of the block and install a tap for a mechanical gage there. This location is accessible, it just isn't convenient. Gage calibration should be confirmed first to ensure accurate readings.
Have you considered that the pressure switch on your light might be out of calibration?
DmaxMaverick
03-18-2008, 08:57
Like said before, if you are going to compare pressures with differing devices, you MUST sample pressure at the SAME location, however inconvenient. Or, use the SAME device to sample at the different locations. There seems to be two objectives here (in regards to this discussion). One is the comparison of pressure samples at different engine locations, and the other is the comparison of different sampling devices. Keep that in mind. Unless you have all your devices calibrated to the same standard, which is an active process, not assuming anything is correct "out of the box", your sample data will be about as accurate as a tabloid news article (sometimes, they get one right, but it's pure luck or coincidence). In the end (as we now see), you will generate more questions than answers. The mere process of your testing will invalidate any data collected.
The GM gage system(s) are notoriously inaccurate, but they aren't generally that inaccurate. If it is inconvenient for you to access the correct sampling location, then you'll have to live with the results you get, and go on scratching your head. If you continue a relative comparison of apples and oranges, your result will yield the same unanswered question at the conclusion.
The mechanical gauge has determined that the readings at the filter and at the turbo are for all practical purposes identical. What you have not determined is the accuracy of the mechanical gauge. Without doing that, it seems that all the speculation is just speculation.
DennisG01
03-18-2008, 10:47
First, I absolutely don't believe there is anything wrong with the engine - from the amount of care that Ron put into building it and the fact that the dash gauge is reading similar to what I saw with the old engine. I agree with everyone that is saying it's simply a case of whether the gauge readings are accurate. Although, both gauge readings do seem to be consistent. If I can find the time to get a reading at the unused port on the back of the driver's head, that should help quite alot to clear things up.
Knowing exactly what the readings are at various locations has never been a priority for me - I know some of you are actually more interested in this than me - and that's OK, I am interested to find out the results, it's just not my main purpose.
This thread has helped me quite a lot to understand more about this 6.5! Thank you!
However, for my purposes, I'm satisfied in knowing that everything is operating within specs, I'll just need a lower PSI switch. But, I will keep up on this and make an appointment at my shop to use their gauge. I can't promise anything, but I will try to get readings at that unused port.
Dennis do you have routing of remote lines crossed? I think at engine base OUT goes to filter head IN then filter head OUT goes to engine base IN right?
That is the way I figured it, too and that is the way I put it together - but I will double check.
Gage calibration should be confirmed first to ensure accurate readings.
Have you considered that the pressure switch on your light might be out of calibration?
Can I verify accuracy with my air compressor? I mean, PSI is PSI, right?
Yes, I have thought about the switch being wrong, although it does seem consistent with the MG (of course, at this point that's assuming the MG is accurate:rolleyes:)
The mechanical gauge has determined that the readings at the filter and at the turbo are for all practical purposes identical. What you have not determined is the accuracy of the mechanical gauge. Without doing that, it seems that all the speculation is just speculation.
ditto.
DennisG01
03-24-2008, 19:09
FOR CLARIFICATION:
At Remote Filter Mount:
RPM MG DG
Idle 13 35
1000 17 38
1300 19 42
And, at 2000RPM, the numbers were 32 and 42.
OK. Final take on numbers gathering here: This morning I went to the garage that did my engine install and used their gauge. When I asked about the accuracy of it, he gave me a little smirk and said "it's dead on - we use it all the time on lots of cars and it's always been accurate". That was good enough for me - besides, I've known these guys for years and they have always proven trustworthy.
Over the weekend, I did the "high idle" mod, so that's why the RPM numbers below seem odd. Except, of course, the 2000 rpm, where it's all up to the steadiness of my right foot :rolleyes:. I only took readings at the filter mount as we've already established consistency between there and the turbo.
------ MG DG
IDLE 12.5 33
1070 25 37
1360 32 40
2000 38 42
Having used a more accurate gauge, it's good to see that the readings have risen. I think we still need to keep in mind that the dash gauge is run off a (typically) less accurate type of pressure sending unit than a good mechanical gauge. In fact, the mechanic and I were talking for a minute or two while I was at the 1070 setting and I happened to notice the dash gauge jump up about 4 psi for about 10 seconds, then back down. During this time, his MG never waivered.
As far as getting a reading at the unused port we talked about, it's not gonna happen. We both looked at it while the truck was on the lift and decided someone would have to be Houdini to be able to easily do that. And I didn't want to pay the labor bill to have him do it any other way - he agreed.
I bought a switch today that is supposed to activate between 8 and 12 psi. We'll see how it works out. If the light is still coming on, I know of one more source for a 7 psi switch.
Again, I appreciate all or your comments throughout this somewhat "minor" post. Thank you!
Thanks for the follow up. That looks much better and makes more sense than other mechanical gauge reading.
Interesting about difference at low flow (idle) but closer at higher flow.
FYI Lawson Products had several different oil pressure switches when I was looking through there book a while back. Lawson products dot com or something like that.
DennisG01
03-26-2008, 05:26
Well, so far so good with the 8-12 psi switch.
Interesting about difference at low flow (idle) but closer at higher flow.
FYI Lawson Products had several different oil pressure switches when I was looking through there book a while back. Lawson products dot com or something like that.
I thought it was interesting, too. Since the stock sender is electronic, who knows how GM has it calibrated. My guess is GM has it calibrated to purposefully read high at low RPM's so they don't get complaints when customers would see their dash gauge reading so low.
Thanks for the link!
... When I asked about the accuracy of it, he gave me a little smirk and said "it's dead on - we use it all the time on lots of cars and it's always been accurate".....
Compared to what? I think the smirk was the most important part of the answer...
Seriously, in the aircraft maintenance business, we have to send everything out annually to a testing service which can trace its accuracy back to the NIST. If the feds come in and can't find a current sticker on my torque wrenches and pressure gauges, I'm busted...
DennisG01
03-27-2008, 05:41
Oh, sorry about that, I was actually paraphrasing a bit. I can see how what I wrote might have been a little misleading as to our actual conversation. He did use the word "calibrated" in our conversation, but to be honest, I don't remember everything he said associated with that (at least not well enough to accurately repeat what he said). What I do remember is that based on what he said I was convinced that this is an accurate gauge. If I was more "in the know" on the process involved, I'm sure I would have remembered more or asked better questions. However, I have known these guys for quite a while and have come to trust them - if they tell me something, I believe them. Don't get me wrong, I don't have "blind" trust - I mean I like to hear explanations, but I do trust them.
Anyone have a picture or remember the view of the engine block oil filter base. In my minds eye I remember the outlet port and I think the bypass valve and knipple but fuzzy on the cup plug with orifice.
I am still wondering about this 1/16" orifice cup plug. I want to say it might be something like this. Oil comes from pump to cooler or bypass then to outer portion on oil filter base. On the outer ring of oil filter base is the cup plug with orifice and the bypass valve both lead to left oil gallery. Oil would go down into filter or adapter and up through cup orifice and if too much resistance up through bypass valve. But normally should go down into outer oil filter can, through media, then up center of filter and back through knipple on block towards the oil galleries.
So does a % of oil always escape filtering through this cup plug orifice? And if so at low flow could that explain an appreciable difference in left oil gallery pressure vs higher flow? comparing remote mount measurement to left oil gallery?
DennisG01
03-31-2008, 08:15
I looked through all of my engine rebuild pics, but didn't find one that would help. However, would a pic of either end of the 90* adapter work? It's just laying on my workbench.
Thanks but I specifically need the engine block view as to understand where oil flows from and to (and or options to flow as in through cup plug and or bypass valve).
If no one has a picture or memory of it to confirm accuracy of what I just posted then I'll try and take a picture.
ronniejoe
04-02-2008, 09:01
http://www.thedieselpageforums.com/photopost/data/500/medium/SplayedMains.JPG
Ok at 6'oclock is is bypass valve. I roughly measured a while back and it opens at 17-19 psi iirc. 1-2 O'clock is oil coming from cooler. The center hole is where filter knipple sends clean oil back to oil gallery.
Not sure where cup plug goes or comes from. Here is diagram of oil system.
If you look at the diagram the drill path straight up from oil pump output. It almost looks like the oil pump MIGHT? feed the oil gallery directly but probably there is plug inline between passages. Oil actually turns towards oil cooler or bypass etc etc.
Not sure what the cup plug does. I was momentarily thinking it might allow a little flow to bypass the filter but then remember oil pressure can't be higher down stream and still have flow down stream.
Back to more thinking.
Sorry tried to upload scanned page of helm manual but can't get size small enough.
If anyone is interested I uploaded it to photo album
http://www.thedieselpageforums.com/photopost/showphoto.php?photo=930&ppuser=18766
chevy1988
04-28-2008, 12:28
Does those engines have a securityvalve in the oilpump as in other engines I've seen so that if the oil gets realy thick (Extreme cold temp sometimes occur here and you dont want to blow the engine then) it will not blow the filter or gaskets in the oilsystem if revved up? Havent yet taken a 6.5-engine appart so much is still unknown to me.
By experience this "ball/spring valve" might get stuck in open possition and engine looses preasure or sometimes even get no preasure at all. The spring has even in som casesbroke and there is nothing holding oil from passing back down the oilpan.
Think I'll eventually get a haynes manual on this engine to, if there is one ;)
Being from sweden, my english might be a bit off sometimes :p
DennisG01
04-29-2008, 05:42
If anyone is interested I uploaded it to photo album
http://www.thedieselpageforums.com/photopost/showphoto.php?photo=930&ppuser=18766
Thank you! It's always good to see things in a picture.
Yes there is a pressure relief valve in the oil pump, main reason is to stop high oil pressure from blowing up the oil filter when someone starts the engine up and revs it up when its really cold out, 15w40 is like gear oil at -40. The only time I have seen a stuck relief valve is from extreme lack of maintaince or contamination (broken engine pieces) but I have seen 1 or 2 broken springs in my 30+ years in this business, it is not a common problem
Ron
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