GM 350 oil pressure issues

[otis24]

1994 GMC K1500, 350 engine. New engine about 5-6 years ago. Maybe 45k on motor. Oil pressure gauge was low. My mechanic put it on a mechanical guage. At cold start-up, it reads 40 lbs. As it warms up, pressure drops to 6-8 lbs.


What are the possible causes? Mechanic did say that he could hear the start of a "tick" in the engine. I think that the plan is to check the bearings for starters.

Any other advice?

 

[skyactiv]

What oil viscosity did you use in the cold winter?

 

[bullwinkle]

Sounds like my (departed) 200K mile+ 350 TBI Suburban-I think mine had bad cam bearings. No knocks, no blowby, no rattles, just super low hot oil pressure in idle, sub 10 PSI. 20W50 fixed it right up, and it even started OK down to 0F! Might need something a little thinner in SD winters, though.

 

[BlueOvalFitter]

1994 GMC K1500, 350 engine. New engine about 5-6 years ago. Maybe 45k on motor. Oil pressure gauge was low. My mechanic put it on a mechanical guage. At cold start-up, it reads 40 lbs. As it warms up, pressure drops to 6-8 lbs.


What are the possible causes? Mechanic did say that he could hear the start of a "tick" in the engine. I think that the plan is to check the bearings for starters.

Any other advice?

Install a high volume oil pump.

 

[zrxkawboy]

Only 45k miles? Was the the engine new, reman, rebuilt by your mechanic...?

 

[RedSpider]

Solving a low oil pressure problem by using thicker oil or using a higher flow pump is like fixing a broken window in winter by turning up the heat.

 

[RDY4WAR]

Does the pressure still increase at least 10 psi per 1k rpm as you rev it? If so, I wouldn't worry too much about it. If you're using a 5W-30 or 0W-30, try a 0W-40 to see if that brings the warm pressure up a little. It's not the ideal way to handle it, but it could bandaid it until you can dig into the issue.

 

[chainblu]

As it warms up, pressure drops to 6-8 lbs.

Is this at idle or running down the road?

 

[BlueOvalFitter]

Solving a low oil pressure problem by using thicker oil or using a higher flow pump is like fixing a broken window in winter by turning up the heat.

True, but it will get the engine by until it can be rebuilt or replaced. I used to do it for friends (and myself) all the time until I could rebuild it for them.
Sometimes I would run Kendall Nitro 70 wt. oil in them.

 

[Racecarfan2]

Textbook main bearing issues. Time for oil analysis see what its holding. My guess Copper.

 

[NitroM3]

well IDK about most of the answer, some are interesting.
You could do a oil sample but based on what I read time to drop the pan and check a rod and crank bearings inspect the oil. But it really looks more like the oil pump? And if it is the cam bearing .... well lets not get to worried yet.

Naturally we all are guessing and without more input from the op that's all it is guessing".

 

[otis24]

What oil viscosity did you use in the cold winter?

5W/30 year round.

 

[otis24]

Only 45k miles? Was the the engine new, reman, rebuilt by your mechanic...?

I think that it was a reman. Bought it from the neighbor. He had a local mechanic install it.

 

[otis24]

Is this at idle or running down the road?

That was at idle. But running down the road the guage on the truck was low. Low enough to trigger the "check gauges" light.

 

[otis24]

The mechanic thinks it may just be the boil pump based upon the fact that there is no engine rattle. Based on Bullwinkle's experience, that may not mean much. I guess my mechanic will know more when he drops the oil pan.

 

[otis24]

Replaced oil pump. Still low oil pressure. Looks like we are going to have to pull the motor and replace rod and main bearings. Since there was no engine noise and the motor only had about 45k, mechanic thought oil pump would fix it. He treated me good on the labor because he felt bad. Just going to have to invest a little more money and squeeze every last ounce of life out of this pickup. Truck has new tires, tune-up (plugs, wires, rotar, cap), new fuel pump, power steering pump, steering box. Can't sell it as is, and can't replace it for what it will take to replace bearings.

 

[mattd]

For future reference, the result of low oil pressure is near NEVER from the oil pump itself, but from either worn bearings (rod/main/cam) or pickup restriction.