Lower oil pressure than normal, things I can check

[john8662]

What a month, can't wait till April is over!!

Anyways, About two weeks ago my 95 6.5 has been showing approximatly 20 psi lower oil pressure than normal. It all started on a monday and has been that way ever since. So, I quit driving it because that an other things that I needed to do (ignition switch). Anyways, this really bothers me, Always when cold, it had 60psi oil pressure, then all of a sudden it has 40, maybee 45 when going down the road. Before it had 60 psi cold, 50 almost 60 psi at 2400rpm going down the highway, and now its 45. Somethings changed. Here is what I have done and checked.

- New Oil filter and oil
- New Oil Pressure switch (same results)
- Swapped in my old fuel lift pump (to see if current one was drawing too much juice, causing the change in readin) same..

I can't seem to find any new leaks (other than the normal seepage on places).

The results were the same before and after the ignition switch change (just happened at the same time I needed the switch).

Other mods on this truck related to oil are the Oil cooler lines from Lube Specialist (the Amsoil guy). And a new oil cooler (factory one). These items have been on the truck for about 6,000 miles. I had to replace the oil cooler because the original one had a burr on one of the theads that wouldn't allow me to install the new line end. So it stripped out, New cooler worked perfectly, just a bad one I guess (expensive though).

The only thing that I can think of that could have a negative affect on the oil pressure could be the turbo. I guess I will just have to drive it an see if I am loosing lots of oil out the tail-pipe. That should tell me. Anyways, this is freaking me out, as I don't want to be on foot if this one breaks, as the 6.2 let me down last week. Grr... Thanks for your help, and suggestions..

John

[gmctd]

Could be wiring\grounds, and\or the instrument cluster.
Try a mechanical gage, maybe tee'd into the turbo supply line - that's 1/4"npt.
Or into the OPS tap, also 1/4"npt.

[C.K. Piquup]

John,I hope some can help you here.My story:I noticed an oil pressure drop like that in my`95 truck.First thought,oil pump or OPS.Checked here,after replacing OPS,and found alot of talk about inaccuracy of guages and talk about mounting aux.guage.But it seemed all agreed there were alot of guage problems and not engine oil pressure problems.I relaxed,kept driving for 4 or so months,then motor went up.I still haven`t gone into the cause,so I can`t say there is a connection.Just be careful.Good Luck to you. CK

[john8662]

GMCTD, I will be getting a mechanical guage today to check for pressure. I can't seem to find a place to get pressure from though.

I looked at the turbo line coming off the front of the block and its buried under all the thermostat crossover and stuff and it doesn't look to me like 1/4" NPT, looks bigger.

Getting to the back of the engine where the OPS is is kind of a pain as well as its covered and I will have to find a tee. I agree that the tap in the block on the back is probably 1/4" NPT and I could probably T into that then mount the OPS back, but tight on room there.

So, my question, could I mount the line to the new guage in the plug on the block above the oil filter?

[C.K. Piquup]

John,I believe you use the guage @ turbo.Just pull supply line from turbo,put the guage on the line.This is just for diagnosis,or use a"T"for permanent mount.

[gmctd]

If that location conforms to standard Chevy specs, it is an oil pressure tap used at one time for big truck gage sending unit. It was available for other stuff, as well, but I have seen the OPS there.

Just for temporary, tho, unscrew the flare nut, top of turbo, remove the npt fitting, insert your tee'd tap there.

[LanduytG]

I have found over the last 165K miles that the in dash gage is and indicator only. If you change sending units you will find that no two are alike. I put a real gage in and the oil sending unit and what you have is normal. Once up to operating temp you should see 40psi at 2000rpm. It will go up some after 2000 rpm but not much. Newer 6.5TD have a different spec at 2000 rpm but I have not been able to find it yet. It is lower do to the oil spray pistons. With my 2000 block I see between 35 and 40 at 2000 rpm. Sometimes gage can cause a person to worry over nothing.

Greg

[JeepSJ]

I had a similar problem on an old gasser engine. I replaced the sender and it didn't change the reading on the gauge. I laid down the $15 for an el-cheapo mechanical gauge at my local auto parts and found that my oil pressure was fine. Stock showed less than 20psi at cruise rpm, and the mechanical showed 55psi.

[john8662]

Well I hooked up the mechanical oil guage at the turbo line, adapted it to work with my guage.

I hooked this all up with the engine warm. I cranked it up, I have 25psi at idle (just what the inside guage says) and 40psi reved up. Damn! I will wait till tomorrow when its cool and try again, see if the readings are different when cold.

Greg,

Since you say that 40psi is normal at 2k why did I have 60psi before and now all-of-a-sudden have 40. At idle before I never saw under 40, now its above the second mark (25 I guess).

So, whats next to try?

Bypass oil cooler?

Replace bypass valve in oil filter mount on block?

Then finally pull pan and replace oil pump?

I also went and renewed ALL the grounds that I could find (underneath, on frame rail to cab) both neg to battery cables to engine block. Renewed with sandpaper to both contacts. No change. Did it just because, not like it has anything really to do with the real problem..

[ 04-26-2004, 02:37 PM: Message edited by: john8662 ]

[gmctd]

Yeah - come to think of it, I found a bad bypass valve where the center spring coil had broken, with result the spring was 1/2 length.
Have a look, and replace the black o-rings with orange silicone rubber type, which GM finally went to, middle 90's.

[gvig]

John,

I bought my 95 as a one owner but very high miles. It had 391,000 when I bought it and the engine had been "refreshed" at around 170,000 but I have no records to show what was done so the oil pump may have been original. The truck had very low oil pressure and I couldn't find an external cause so I pulled the pan and checked the crank. No damage but the bearings showed some wear, not bad but definitely not new spec for wear.

While I was in there I took apart the oil pump and what I found was scary. Severe wear. So I replaced it but had some difficulty finding the correct pump. OEM pump was much smaller till I moved up to a 98 pump, then the case and rotor were the same length. Now I have around 60 when cool at 2000, going down the road at normal temps and about 2000 I have right at 40 or just under. Idling hot I have just over 15, maybe closer to 18.

Would like more but with good bearings and a new pump that is all I get on a stock gauge. Good luck.

[john8662]

An Update...

I finally got the right parts to do the job. I started off with a complete flush of the oil system, put in flush, drained oil, new fresh oil put in it, no change in pressure. Heck I figured if there was some crud that I probably got rid of it, its clean now. Next, I pulled the front driveshaft for the 4x4 and pulled the oil filter adaptor out. Took a look-see, everything in order here, then I pulled one of the connectors on the oil cooler lines I got from the Amsoil guy. I did find a problem..

I was a little bit leary about the installation of the lines with the copper washers that were supplied to keep from having to tighten the lines up too tight to the 90's screwed into the block. I found that while tightening up on of the washers on the initial install that one had slipped, and it was cutting about half the flow through one of the lines. Not good. But, I think that might be the cause of my problems. I will post pic of the washers sometime later. I then put everything back together W/O the dern washers, tightened it good, should have done this the first time. I then grabbed the trusty craftsman screw driver and stabbed the "oil cooler bypass valve" and pulled it out of the block in the oil filter mouting area. I installed my new one, then put everything back together, topped off the oil, cranked it, its still low. So, next comes the pump, maybee the restriction caused the pump to fail early or a bypass built in the pump to fail?

The next question for those who know. How can I get the pan off an IFS 4x4 truck? Is there enough room to disconnect the exhaust and lift the motor (w/o the motor mount bolts in) up to get the clearance? Of course w/o disconnecting the trans or t-case. Or is this one of those lovely GM deals where I have to yank the engine out to replace an oil pump?

Let me know, thanks, would have liked to go to the Rendezvous this year, but I have the money but not the roader..

[ 05-18-2004, 05:51 AM: Message edited by: john8662 ]

[john8662]

The new oil pump is intalled and I got the burb back together. The process of getting an oil pump installed was put off because I needed to order everything (the oil pump) and I installed the Stud Girld Kit from DSG since I was there, and had a no-crack block on the main webs.

Anyways, the good news, I have great oil pressure again. It idles 60 psi cold and runs 60psi down the highway. When hot it runs about 35psi at idle and 55 down the highway (2k rpm at 65mph). Thanks for the advice of what to check. Its back on the road again...

[tom.mcinerney]

Nice work , John. Crack-free webs + hi oil pressure = good news.

Q.1.) If remove u-tube and front diff, is that enough to drop pan?

Q.2.) Did you open up oil pump? Any idea if problem was at pump or bypass valve?

[john8662]

Tom,

I didn't have to complely remove the front differential. I just took out the 4 big bolts that hold it up there. There are two on the drivers side, and two on the passengers side. You'll have to remove both the skid plates to get access to everything. I took more apart that I needed to at first thinking I had to completly remove the front differential. But all you need to do is let it drop down. It won't fall out, it will just hang lower, just enough to confortably get the pan off. So, now I know you can get the pan off a 4x4, don't know about a 2wd.

Yeah, I took apart the old pump. It had some wear and looks like it had been hot on one of the gears inside of it. I am sure that it was the bypass/regulator valve in the pump that had gone bad. I think the pump has been flaky ever since I had purchased the burb. Because it always ran high pressure, sometimes spiked to 80psi (I thought it was just electrical). But now I know differently, because all-of-a-sudden it quit putting out the pressure and capped off at 40psi when cold (where it had been 60psi), and just went down from there. I caught it just in time. From going and driving some other 6.5's, I have noted that 25 to 35 psi at idle is good, thats what I have now, but going down the highway I get the 55 to 60 when hot, which the old oil pump quit doing.

So, one interesing point I can make, is that the lower oil pressure at idle I thought to be a problem really wasn't. Just the not so good highway pressures and cold start oil pressure that had dropped that really scared me, and for good reason (a max of 40psi no matter what), now its 60psi cold, 55psi at highway, big difference there.

Funny thing is I liked the pressures that the old pump put out when it worked kinda right, but turns out, it wasn't right.

Now, the oil pressure readings and variations (between rpm's, idle, and highway speeds) of my 6.5 match what my 6.2 has done for years. So I know things are normal now, now back to they way it was before the pump went bad, because I think it was bad before it quit putting out higher pressure (flaky bypass/pressure regulator valve).

[ 05-29-2004, 11:06 PM: Message edited by: john8662 ]

[catmandoo]

beings your on a low oil pressure issue here,has anyone noticed a drop in pressure when turning on the lites,mine loses about 5lbs on the factory gauge,when i turn the headlites on,and my gauge reads 45 cold and 25 down the road,i need to do a mechanical test to see how far off it really is.

[john8662]

catmandoo,

your engine starts up at 45psi bone cold? and you see 25psi oil pressure running down the road (what RPM)? Not just at idle, because 25 at idle on a HOT day is normal (as I discovered)? Yeah, if thats right, then you should probably check with a mechanical guage just to make sure its not just another one of those electrical grimlens.

[catmandoo]

when hot it idles at about 15-20 by the gauge,but i don't believe it,need to get out the mechanical test gauge we used in my dads shop,

[aj neireiter]

when I first bought my 6.5td it had 58,000 miles on it and it had great oil presure. With time I noticed a loss of presure, talked to the mech.He said that everything is ok. 18psi hot at idole, 35psi hot at 2000 rpm. Now I have 150,500 miles and two days ago it started to stall at low idole. after reading several posts on this web site and some great advice, I changed the OPS and my oil presure is back up to 35psi idole, and 65psi at 2000rpm. THANKS FOR ALL THE ADVICE!!

[panchosteam]

Hi guys, about aweek ago the belt on my truck broke on the freeway,i was doing like 70 or 75mph,when althe suden i could smell some kind of like burnt rubber,looked at the gauges didn't see any abnormal stuff, looked again,and then saw the teperatue raising,no oil pressure,so like about 2 or 3 miles after(when i could)stopped on the side of the freeway, turned engine off and pop the hood,what i saw was the expected,broken belt,oil alover the place,two kinds of oil,motor oil and power steering fluid,after this im seeing oil pressure like john's, at iddle:just before 40,at high way somethimes over 40,i think i remember seen it back to normal(about 60) but then went down again,i also notice that if is just iddling and i give it diesel about quarter pedal the turbo will whistle, and then a weird noice kind of vacuum like,should i be worried ?
Thank you guys.
1984 GMC SIERRA CLASSIC PICK UP NOW WITH 6.5TD AND HEATH'S TURBO MASTER

[whatnot]

Originally posted by panchosteam:
Hi guys, about aweek ago the belt on my truck broke on the freeway,i was doing like 70 or 75mph,when althe suden i could smell some kind of like burnt rubber,looked at the gauges didn't see any abnormal stuff, looked again,and then saw the teperatue raising,no oil pressure,so like about 2 or 3 miles after(when i could)stopped on the side of the freeway, turned engine off and pop the hood,what i saw was the expected,broken belt,oil alover the place,two kinds of oil,motor oil and power steering fluid,after this im seeing oil pressure like john's, at iddle:just before 40,at high way somethimes over 40,i think i remember seen it back to normal(about 60) but then went down again,i also notice that if is just iddling and i give it diesel about quarter pedal the turbo will whistle, and then a weird noice kind of vacuum like,should i be worried ?
Thank you guys.
1984 GMC SIERRA CLASSIC PICK UP NOW WITH 6.5TD AND HEATH'S TURBO MASTER Do you have a belt driven vacuum pump? If so, I would check that first.

[panchosteam]

Hi whatnot,yes i do have a belt driven vacuum, not in use,i also have the one that came off my 6.2 engine,wich was mounted on the rear passenger side of the engine,this is what im using for my truck not the belt driven vacuum,at first i had the belt driven connected to the part that controls the transmission on the side of the IP, after this happen (broken belt)i decided to switch to the old one just to check for differences,i sure did notice something, it shifts like it did before(when i had my 6.2) i don't know yet wich will be the one i'll use yet
the belt driven vacuum used to shift faster and you could feel like a bump when it did, i think it made the transmission a little crazy(too much pressure i think) and this is the history, should i be worried about the oil pump issue? thank you for your quick response.

1984 GMC SIERRA CLASSIC PICK UP NOW WITH 6.5TD AND HEATH'S TURBO MASTER

[whatnot]

If you aren't using the belt driven pump then just remove it. A belt for a '92 or '93 will fit and is cheaper.
My brother's truck had the vacuum pump freeze up and break the belt.

Someone else will have to answer your oil pressure questions. (If you have an electrical gauge, you might want to put a mechanical gauge on it to verify it isn't just a gauge problem first)

[panchosteam]

Thank you WHATNOT,i guess i'll try the mecanical gauge and go from there,i was tinking of keeping the belt driven vacuum just for other accessories latter,if this vacuum fails, could i just keep it there or it wont move because the bearing will freeze?
1984 GMC SIERRA CLASSIC PICK UP NOW WITH 6.5 TD AND HEATH'S TURBO MASTER