Dancing oil pressure gauge?? I'm getting scared now...HELP!

[Randee of the Redwoods]

The truck is still running like a smooth operator, but on the way home from work today, the oil pressure gauge seemed a bit happier than usual. Usually, I noticed about 60+psi oil when starting the truck cold. After it warmed up, about 50 or so. Today, it started off at about 50(odd), then shot up to 70(odder), then rested to it's usual 60 all the while the needle moves as engine load changes(signifying a response to changing oil pressure. This needle dancing continued all the way home with the reading dropping to as low as 40 at one point while I was climbing a hill. It really scared the crap out of me. Then, wouldn't you know it, it set back at 50 or so until I parked at my apt, where, at idle in park, the gauge was reading 40psi oil pressure. PUMP OR SENDER???? I'm almost afraidto drive the truck now for fear the oil pump will go south on me. With 181+ on the ticker, I'd expect it to maybe be in the neighborhood for replacement. BUT, in following with the flaky oil pressure gauge senders in the 6.2's, I figured I'd ask first before panicking(sp) since I could be worrying about nothing. Anyone? :eek: :eek:

[mhagie]

Randee, You can do as you chose but I have a mechanical gauge as backup for both water temp and oil pressure, for the exact reason you describe.
Gm trucks are notorious for false reading gauges, I trust them not even a little bit.
It would be my guess that a quality gauge such as Isspro,or a good name brand elec would also give good quality readings but OEM are quite suspect.
In short install a quality aftermarket gauge so you know exactly where your at pressure wise. :D

[Randee of the Redwoods]

So you're leaning towards a bad sender? Whew. That's a load off. tongue.gif
Where's the gauge sender located? I might replace it anyway. And would I ok to assume that the pump truly is ok and should be ok as long as I take care of the engine? Truthfully, I've never heard any mention of the oil pump anywhere on these boards so I'm assuming they are at least modestly stout and can last a long time bordering on indefinately.
And what's up with all those vehicle model years in your sig?? You trying to build the perfect truck one model year at a time?

[mhagie]

Randee, Note the word rustbelt,here with all the chemicals used for snow melt it also does a little (lot)of body melt/RUST.
The numbers game is as follows 75 frame,77 front axle,79 posi rear axle,80 silverado front clip 84 cab from Texas,85 box from same place, 83 6.2 engine accesories and transfer case,and last but not least a 94 6.5 reman from The Diesel Depot.
As it is evident it would have been cheaper to go to Texas and purchase a truck I would have missed out on all the fun Of building same. :D :D :(
We have 95's with rust bubbles above rear wheel openings on box. :( :mad:

[Randee of the Redwoods]

So far, so good. Only real rust is underside of the hood lip on the front edge. I'll hit that soon.
So you still think the pump is ok and it's the sender giving me problems? Is it the same sender for the fuel pump?
I'll sell you my 84 Jimmy so you can have the nice gray cloth 88 seats and steering wheel(if you can get it back off).

[mhagie]

Randee, I have to admit that my experience is limited kind of like yours to the older pre computer models.
But I do believe that there is an excellent chance your problem is related to sender.
There are only three possible connection points on engine to moniter oil pressure.
First and most likely is on back of block directly behind the mating point of top side of head and intake manifold,historicly that has been the point of choice by GM. it is a PITA to access thats why they use it. :mad:
Second, and a popular place to hook an aux gauge is a 1/4 NPT pipe plug just above the oilcooler lines, drivers side above oil filter. Small blocks use OPS for choke here.
Third and I believe where the later turbo models tap to feed oil to turbo is front side passenger head about 2" down from mating of head and intake that also is a 1/4" NPT plug.
My experience is zilch with the later models but I would not be surprised in the least if the OPS for the pump and the OP sender are one and the same.
By sticking my neck out here maybe it will entice someone to jump in and correct me,either way you win. Again I STRONGLY recomend you install an aftermarket gauge.
Case in point my friend has a 89 1/2t w/5.7 with factory gauges his shows 60psi above idle with a slight drop to about 50 at idle, to which I say bullcrunchies, I've had high performance small blocks before and even with high output pump at idle about 35-40 is about it with closer to 30 being the norm.
Sorry about the length of this post but I am totaly anal about the lack of trust one can have with OEM gauges.
Don't forget to check all underhood ground connections as they can cause some very wierd problems. :D

[Randee of the Redwoods]

I hear ya on the underhood connections. I'm in the process of replacing all battery cables and grounds as the originals were pretty ghetto at best. I'm now charging at 14 volts, up from 9, and can keep a good reading above about 12 with lights, a/c, blower motor, etc on. I think the replacement of the long cable and the starter cable will finally bring the electrics back up to snuff.
To remark on your remarks. Yes, I am limited to the mechanical motors, but I'm learning. The little troubleshooting I do now goes a looooong way toward repairs in the future.
I'll go with the sender for now and look into a replacement. I like the back up gauge idea and am looking into it. I don't want redundant gauges or dead gauges, so I'm planning on hookups so when a trouble arrises, I can quickly attach a mech gauge and continue troubleshooting.
For now, I'm just happy it starts.

[Randee of the Redwoods]

Oh yea...what are the semi-relative oil pressure readings I should be seeing? If I know what to expect, then I'll better know if the gauge is lying.

[rjschoolcraft]

I would agree that it is probably the sender. These pumps are pretty robust...fairly large end clearances (relative to what my aircraft experience is) and the housings are made from cast iron (instead of aluminum) so the thermal expansion is close to that of the steel gears...you don't get much wear. Usually, they have to ingest some foreign object to damage them. The only thing that could cause what you describe is a sticking regulator...but that's not likely.

Mine will carry about 40 psi at idle warm.

[whatnot]

I think that the OPS is the same one that runs the lift pump since there are 3 wires going to it. (it is just behind the fuel filter)
I don't know if the wiring is the same but on a Pontiac Transport that we have, one of the ground wires broke and the oil pressure gauge went to the top and stayed as long as the engine was running. You might just have a loose ground wire somewhere. If it is a bad ground, there is a chance that something else uses it too. maybe if you try turning stuff on and off you can cause the gauge to move.

[rjschoolcraft]

I would like to correct my previous post.

Oil pressure at idle COLD is 40 psi.

At idle warm is about 30 psi.

Cruising at highway speed is slightly over 40 psi.

[C.K. Piquup]

General note:low voltage will cause guage freak-out in computer trucks.Anything from a bad ground to battery(s)to Alt/Vreg.Also bad part in circuit.

[StephenA]

Hi Folks, It's sooooo nice to find you guys! I just became a new member looking for (among many other things) an explanation for my dancing oil guage, which started acting like Randee's just yesterday. Glad to know the pump is robust steel instead of aluminum. Jim (who handled my sign up in just a few hours) recommended using a multimeter to measure the output, thereby establishing if it's the sender or the gauge. I'll post what I find. Hope it's something simple! ;)
P.S. I just fixed my windshield wiper module by resoldering the connector (probably old stuff on this forum, but if not, it's REAL easy and even works when it's raining!)

[Randee of the Redwoods]

I, too, was relieved to hear of the tough parts in these diesel engines. I knew paying for this website was a good idea.
Stranger things have happened I know, but I'll bank on the off beat oil sender for now. The same thing happens on my 6.2, although it just goes south alltogether rather than giving warning signs.
I'm also going to follow someone elses recommendation on regrounding the gauge cluster. I have the wiring digrams in my Haynes manuals(soon to be getting the Helm's set). Hopefully this will fix my dancing voltmeter as well.
StephenA, does how low does your gauge go during normal driving? Mine reads as high as about 70psi(?) to as low as what looked like 38psi. The low reading is what originally scared me, but after it hit that low reading, it worked it's way back up to about 45psi and I neve saw 38 again.

[StephenA]

Hi Randee, - Before it learned to dance, my gauge always moved gradually from 35 to 45 or 50, but bear in mind, -I'm running Mobile 1, 15w50, so my viscosity does a temperature swing that's a bit different than normal, nonsynthetic oil. I'll get a chance to check my sender voltage this weekend and let you know what I find. I have the Chiltons, and in the Haynes I could only find the book on diesel motors for my 92. I'd love to find the Helms, and I'm checking around for original shop manuals from a defunct dealership. Let me know how the grounding goes- that sounds like a winning approach.
My gauge has never gone below 35 so far, but the quick drop down from 55 startled me not a little. In a quick change like that, it figures to be electrical, me thinks. Searching this wonderful forum, I see many references to this same problem we're seeing, attributed to electrical malfunction, and not to actual loss of oil pressure, thank heavens. My oil cooler lines are a bit suspect, as is the adapter for the oil filter, which leaks a bit. When the oil cooler lines go, they dump oil in a hurry, hence my original nervousness with the gauge fluctuations. An additional analog guage sounds like a great idea, since I plan to run this truck for as long as diesel is available...
I've had various Powerstrokes and never thought I'd get hooked on this engine, but it got under my skin, along with the rest of the package on this 92 4x4, and I'm just stoked on the value & performance it delivers for the $$. One sweet truck...

[StephenA]

To get back to Randee, I was going to check the voltage readings from the sensor this weekend and post them, but since I found this great website and got some history on this and other issues, the gauge decided to sit up & fly right with no more dancing, just steadily reading correctly.
Amazing how a little understanding sometimes seems to blow off the gremlins... I'll post the readings if they return.