Oil Pressure Problem

chevrolet

#1

I have a 1986 Chevrolet El Camino with a small V-8 engine. The vehicle has 150,000 miles on it. It starts and runs fine. It does not use oil. My problem is the oil pressure. After the car runs for a short time, the oil pressure starts dropping. It will drop all the way to 0 if I let it. I have had the sending unit replaced and it did not help. I have had two mechanics look at it and they have not been able to help me. One checked it with a mechanical gauge and confirmed the low pressure. He suggested a higher weight oil and an additive. The other mechanic’s solution was to raise the idle speed. I have had this vehicle since it was new and always kept the oil changed and all other maintenance done. I would like to keep the vehicle and complete any repairs necessary. My question: Is the engine repairable economically or does the engine need to be replaced and what is causing this problem. Any help you can give me would be appreciated.


#2

I had a similar problem years ago with an engine (GM 350) that was running fine. It’s only fault was that it lost oil pressure as the engine heated up. I contemplated using a heavier oil but opted instead to replace the oil pump. I chose a high pressure, high volume oil pump and it worked like a charm. My oil pressure was more stable after that even though it still lost some oil pressure when the engine reached operating temps. You might just need a high volume pump but I don’t have too much experience with them so I can’t recommend one.


#3

In my expierience, when the oil pressure drops to zero the longer the engine idles, it usually points to worn rod and main bearings.

Tester


#4

I agree with @Tester‌

I think the engine is tired and due for an overhaul


#5

The engine is probably tired but an oil pump and screen might breathe some life into it. The optional high volume pump will be an additional benefit if you can get the oil pan on without it hitting.


#6

Just changing the oil pump to a high volume unit is a band-aid. Even if it works, it won’t last too long. With 150,000 on it and confirmed low oil pressure, an overhaul will be a better, longer-lasting repair.


#7

In my expierience (sic), when the oil pressure drops to zero the longer the engine idles, it usually points to worn rod and main bearings.

And if the crankshaft bearings are worn the camshaft bearings are not far behind.


#8

Agreed; the engine is getting tired. Odds are if the oil pan is dropped and some bearing caps removed you would find the crank bearing surfaces scrubbed away.


#9

I also agree that the engine is too tired.

Engines use something called “sleeve bearings”, which are two curved metal “sleeves” that surround a smooth turning surface. There exists within the parts “oil channels”, paths for the pump to push the oil through to feed it directly into the spaces between the bearings and their corresponding spinning surfaces.

Oil pressure is maintained by the pump forcing oil through the wee spaces between the bearings and their corresponding surfaces. When the spaces get too worn, the oil flows through too easily and the pump has trouble maintaining pressure. Sort of like trying to keep a balloon inflated with a pinhole.

Try a higher base weight oil. You have nothing to lose.


#10

Depending on the accessibility of the oil pan, and as long as the engine isn’t making any mechanical noise, you may be able to get away with throwing a set of rod and main bearings in the engine without doing anything else. I would do a compression test and make sure the engine is worth ‘saving’ Otherwise I would just drive it until it cannot be rescued with thicker oil and starts making noise, then look for a used 350 or rebuild the one you have.


#11

I would advise not taking any long trips away from the house. It’s possible that when wear gets to a certain point a rod bearing shell could swap sides; meaning 2 shells on one side of the journal.
When, or even if, this happens there will be a catastrophic bang and that will be the end of it.


#12

Does the volt meter indicate <13 volts when the engine is running? Not to discount your mechanic Re the pressure test but there is a ground for the instrument cluster near the brake pedal that can become corroded and cause poor continuity which will cause the gauges to indicate well below actual.


#13

Years ago I had a 71 Ford pickup with the small 302 and had oil pressure problems. When started cold would have about 35- 40 psi and would drop to zero on a mechanical gauge. I had a friend who was a retired mechanic and he installed new rod and main bearings. You could see that the bearings were worn, I forget but one layer was gone ( either the lead or the copper ). The crank was ok, no marks etc.
and he cleaned the oil pump screen but did not look to bad, After install we got 50 psi when cold at idle and would only drop to 25 psi when hot, but shoot to 40 psi at 2000 rpm. Before we started the engine he removed all the spark plugs and cranked it until we got some pressure on the gauge to make sure the new bearings had oil with no compression strain on them.

I ran the truck like this for years and no more oil pressure problems.

He never did touch the cam bearings…I ran 15W - 40 oil in it as we live in hot Florida. I did sell the truck for 500.00 down the road to someone in the neighborhood…I know he ran it for a few more years like this but I ended up moving so lost track of it…

My mechanic friend did not want anything for the job, except for the parts, but did give him a nice tip and dinner.


#14

@Rod Knox: A good thought, but the OP says a mechanic actually measured the oil pressure. So it looks like a worn engine.