Chevy 350 making only 3 to 5lbs oil pressure idling when warm.

[WillBrinkhoff]

I have a 1996 chevy 1500 with the 350 5.7, it burns a little oil too. The oil pressure has slowly been getting worse over time, now when warm it only makes around 3-5lbs when idling. As embarrassing as it is, one time when I first changed the oil myself, I started it up with the drain plug out and backed it up to get the catch pan out from under it, could this have caused the issues to start?? Also, I run 10w-30 Parts Master oil and a Wix 51061. My question is will running 20w-50 fix my issues and keep the truck on the road? I don't want it blowing up.

 

[AandPDan]

What are you using to measure the oil pressure? Try a mechanical gauge if you haven't.
Any ticking or knocking?

 

[ripcord]

Have you put an accurate oil pressure gauge on it to confirm the actual pressure? If it's an accurate measurement, I would definitely go with a heavier weight oil. 20w-50 is a good idea in that case, but it will not "fix" anything, but it may let you keep it alive longer. Obviously, avoid idling this truck.

I would be saving up for a new engine for sure.

 

[WillBrinkhoff]

What are you using to measure the oil pressure? Try a mechanical gauge if you haven't.
Any ticking or knocking?

No, I have not, but when idling it bounces off the bottom to maybe 3 to 5lbs.

 

[skyactiv]

Don’t the cam bearings get worn out and cause that on SBC’s?

 

[supton]

Sounds to me like she's getting worn out. Maybe see if a shop can drop the pan, mic the bottom end and rods, and if they can roll in new bearings. I think there's a cross member in the way though, so it may not be as trivial as I make it sound. Might want to do a compression test first, perhaps the walls match these bearings. Getting a mechanical gauge onto the oil is a good idea, though.

I'd step up to an xW40, see if that helps it a bit, xW50 seems thick but perhaps it's just fine.

 

[LDM]

No, I have not, but when idling it bounces off the bottom to maybe 3 to 5lbs.

That is probably because the air core gauge is worn out. You need to check this with a proper gauge, not rely on the old dash gauges that are notorious for breaking after 25+ years. My brother has a 97 K1500 with the 350 and the only reliable gauges left are the speedo and the gas gauge.

 

[WillBrinkhoff]

That is probably because the air core gauge is worn out. You need to check this with a proper gauge, not rely on the old dash gauges that are notorious for breaking after 25+ years. My brother has a 97 K1500 with the 350 and the only reliable gauges left are the speedo and the gas gauge.

I will check when I get home from work.

 

[Exhaustgases]

You really don't know what the pressure is until an accurate non electrical pressure gauge is used to check it.

 

[wpod]

How many miles on the engine and how was the engine maintained? Check with a mechanical gauge is a must.

 

[atikovi]

Is it like that only when hot or also when cold. If it's not knocking, I wouldn't worry about it, an engine at idle is under very little stress. As long as it has SOME oil pressure and it goes up as soon as you step on the gas, it's fine. It not likely a 28 year old rust belt truck is long for the world anyway. Maybe change to 10W50. Does that engine have a pressure relief spring that may be weak or broken?

 

[twX]

LS engines can have an issue where the oil pump pressure relief valve gets stuck open. This results in low oil pressure at warm idle when the valve should be completely closed, but normal oil pressure at higher rpm or when the oil is cold enough.

If oil pressure is also lower than normal at higher rpm, you might have a different issue, like an oil pickup o-ring, or worn bearings.

You could use a thicker grade of oil as a temporary band-aid, to increase oil pressure a bit until you fix the problem.

 

[bullwinkle]

LS engines can have an issue where the oil pump pressure relief valve gets stuck open. This results in low oil pressure at warm idle when the valve should be completely closed, but normal oil pressure at higher rpm or when the oil is cold enough.

If oil pressure is also lower than normal at higher rpm, you might have a different issue, like an oil pickup o-ring, or worn bearings.

You could use a thicker grade of oil as a temporary band-aid, to increase oil pressure a bit until you fix the problem.

‘96 350 SBC isn’t an LS… Low oil pressure IRL usually means lifters start ticking/collapsing at hot idle, not enough pressure to keep them pumped up. By the time I sold my 200K+ 350 ‘94 Suburban, I was running 20W50 & STP Oil Treatment in it to keep the hot oil pressure up!

 

[Cujet]

I agree with the above, try a mechanical oil pressure gauge.

I also think it's not uncommon for older SBC engines to lose oil pressure as time and miles pile up. This is especially true if some fuel dilution happens to an already thin oil. My old shop had a good number of SBC powered trucks and oil pressure loss was common. We stepped up the viscosity and kept them running far beyond what we expected to get.

I had one engine failure that was notable. The oil pressure was zero at idle, the main bearings would start to squeal as the crankshaft oscillated around the bearings. Revving it up solved the problem for 20 seconds or so. It lasted like that for some time, and was fine on the highway. But eventually the engine damage was too severe and the engine was rebuilt.

 

[tiger862]

Normal for SBC with high mileage. Cam bearing goes first then rest. I've seen people put 20w50 as well as high volume oil pumps however that is a bandaid to further damage engine. Wish I had pictures of my dad's 350 after he ran the bandaid for a couple of years then oil pressure dropped to 0 at idle and 20 on highway. Motor wasn't worth rebuilding.

 

[Marcozi]

Does the oil pressure light come on when the pressure is low? Oil pressure switches typically close when the pressure is about 8psi or less.

 

[WillBrinkhoff]

Does the oil pressure light come on when the pressure is low? Oil pressure switches typically close when the pressure is about 8psi or less.

The light off and I put an actual gage on it, the psi never dropped below 3 but never passed 6 when idling warmed up.

 

[TwoTires]

If that is a true oil pressure measurement, then every time you run it you're more then likely making it worst. Old school motorcycles would suffer this when new, that's why riders "Blipped" the throttle when stopped. I would hold the idle up, and run it into a competent shop ASAP. Forget all this changing weight oils as they might just make it worse. That's NOT a way to fix mechanical problems. You could be looking a minor rebuild now, vs. not repairing it and sooner than you think replacing the engine for a lot more money.

 

[ripcord]

Disagree with previous post to a point. IF you do not intend to rebuild this engine right away, go ahead and change to a higher viscosity oil. Doing so will help it live longer by reducing metal to metal contact.

 

[Cujet]

That's NOT a way to fix mechanical problems.

What? Revving the engine and using high viscosity oils don’t fix the problem?