Oil pressure questions.

[attagrl]

Hi!
I'm new here so I hope I'm posting in the right place. I did a search and couldn't find an answer to this specific question but please forgive me if I missed it.

I have a 1994 Chevy box truck on a GP3500 van. It has 125k miles on it. It's my home, I love it and I do hope to keep it running as long as I can.
I'm aware that the oil pressure on these can run on the low side.
The oil pressure starts out fine when the engine is cold, drops low at warm/hot idle and then goes back up a bit with my foot on the gas.
I just had it in at the mechanic and they changed the oil for a heavier type, which helped a little but it still is running below what they recommend (I forget the actual numbers but can find out if it is important to this forum).
They suggested I might have them drop the oil pan and check the pump and o-rings but stressed that it might not solve the problem and they recommend putting in a new engine because mine is 'tired'. They quoted me $1100 for the oil pan inspection.

I would love to be able replace the engine but it's not within my means at the moment.

My question for you more knowledgable folk: is this worth doing, given that it may not help at all and I'll then be out over a thousand bucks and still need a new engine?

It's possible that a friend and I could do it ourselves but I personally have no prior experience - except that every auto job I do for the first time takes many times longer than anticipated and usually also needs a tool or part I don't have.

[MountainManJoe]

Welcome attagirl.

Which engine does your truck have? The 5.0L, 7.4L or 6.5L diesel?

It's up to you if you want to have the inspection done. Yes, there is the risk of not finding anything.
Given it's a 30yo truck, I would not want to put a great deal of money into it. Certainly not worth an engine. That money is better spent towards a replacement vehicle.

Did anybody verify your oil pressure by measuring it with a mechanical pressure gauge? GM released a technical bulletin saying the gauge in the cluster is NOT accurate:

https://charm.li/Chevy%20Truck/1994/G%2 ... 0Concerns/


Engine Oil Pressure: Specifications Normal Oil Pressure Lbs. 18 psi @ 2000 RPM & 24 psi @ 4000 RPM.


Causes for low oil pressure:

- Slow idle speed.
- Incorrect or malfunctioning oil pressure switch.
- Incorrect or malfunctioning oil pressure gage. Replace with proper gage.
- Improper oil viscosity or diluted oil. Install oil of proper viscosity for expected temperature, or install new oil if diluted with moisture or unburned fuel mixtures.
- Oil pump worn or dirty.
- Plugged oil filter.
- Oil pickup screen loose or plugged.
- Hole in oil pickup tube.
- Excessive bearing clearance. Replace if necessary.
- Cracked, porous or plugged oil galleys. Repair or replace block.
- Galley plugs missing or incorrectly installed. Install plugs, or repair as necessary.

[attagrl]

Hi Joe,
Thanks for the response!
It's a 7.4L gas and yes, they tested the oil pressure with a mechanical gauge. The rating after the oil change was at the low end of what's considered tolerable for this engine, if I remember correctly.
It seems any one of the issues listed could be at fault but as you say, it's old enough (the mechanic also flagged up a stabiliser bar that needs replaced).

Given that I agree it doesn't make sense to put over $1k into a truck this age, can you tell me if it would be downright dangerous to drive it with what may or may not be truly low oil pressure? Other than this issue it starts and runs great. If I run it into the ground am I likely to have something blow up.. or just... stop?

[MountainManJoe]

the oil system is vital to an engine. It's like your blood. If the pressure is low enough, the engine will fail quickly. It could be a quiet seizure, or it could smash itself to bits.