Oil Pressure
Thread Starter
Heel & Toe
Joined: Apr 2020
Posts: 23
Likes: 3
From: Oakdale NY
Oil Pressure
I have a baffling oil pressure situation with my 80. When the vehicle starts cold the oil pressure reads 35 to 40, I use 5/30 oil. Once its driven warm the pressure stays around 30. BUT stop at a light or stop sign the pressure gauge goes down to 0. Start driving and the pressure gauge goes back up to 30 again, stop and back to 0 again. It's been a constant problem. I have done oil flushes, replaced the sending unit twice, replaced the oil pressure gauge, dropped the pan and replaced the stock oil pump and pickup with a Melling high volume pump and pickup. To be safe I have also removed the valve covers to ensure oil is reaching the heads, it is, and I have no tapping lifters at idle or driving. Any ideas in this regard are welcome. Thanks and hope everyone enjoyed their Fathers Day.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
When your engine is cold from sitting, 90% of the oil capacity is in the pan waiting to be pumped. After a warm-up, lots of oil remains in the block & heads.
I hope you set your pump screen about 3/8" off the bottom. And not at a angle that the screen will starve for oil. Too late now, but a gob of Silly Putty on the pickup screen then dry / test fit the pan w/o a gasket will verify the clearance.
When you had the valve covers off, was there excessive amounts of oil in the valvetrain area? Some head designs collect a awful lot of oil upstairs before releasing it through the drain holes. And that might be something to check. There is one drain on each end of the head. Make sure its not blocked by anything other than a head bolt.
I hope you set your pump screen about 3/8" off the bottom. And not at a angle that the screen will starve for oil. Too late now, but a gob of Silly Putty on the pickup screen then dry / test fit the pan w/o a gasket will verify the clearance.
When you had the valve covers off, was there excessive amounts of oil in the valvetrain area? Some head designs collect a awful lot of oil upstairs before releasing it through the drain holes. And that might be something to check. There is one drain on each end of the head. Make sure its not blocked by anything other than a head bolt.
Instructor
Joined: Feb 2017
Posts: 136
Likes: 28
From: Liberty Island
Have you verified your PSI with a mechanical gauge?
There is a port on the top of the block just to the drivers side behind the distributor.
Has your engine been rebuilt?
Same results before and after the oil pump swap? I am also running a hv melling pump and pull 70 psi at cold idle on the stock gauge.
There is a port on the top of the block just to the drivers side behind the distributor.
Has your engine been rebuilt?
Same results before and after the oil pump swap? I am also running a hv melling pump and pull 70 psi at cold idle on the stock gauge.
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Wouldn't dream of running such a light oil in a Gen 1 SBC.
I run 20W-50.
I run 20W-50.
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Dr. Detroit
Joined: Mar 2012
Posts: 10,093
Likes: 4,019
From: New Braunfels Texas
Hookup a quality oil pressure gauge under the hood and verify.......I don't trust any original Corvette gauges unless they are calibrated.....
Your oil pressure cold is somewhat low....so there is a chance that you have scrubbed some of the babbit.......
Hook the second gauge up.....if it still is low....you are in for set of bearings.
Jebby
Your oil pressure cold is somewhat low....so there is a chance that you have scrubbed some of the babbit.......
Hook the second gauge up.....if it still is low....you are in for set of bearings.
Jebby
Thread Starter
Heel & Toe
Joined: Apr 2020
Posts: 23
Likes: 3
From: Oakdale NY
Thanks for all your resonses. The engine is a crate motor installed by the prior owner in 2002. It has 20000 miles on the engine, stock except for edelbrock carb and manifold with a set of headers. I will try going with a heavier oil, at least 10/40, and see if it makes any difference before I try more extensive ideas.
Dr. Detroit
Joined: Mar 2012
Posts: 10,093
Likes: 4,019
From: New Braunfels Texas
Thanks for all your resonses. The engine is a crate motor installed by the prior owner in 2002. It has 20000 miles on the engine, stock except for edelbrock carb and manifold with a set of headers. I will try going with a heavier oil, at least 10/40, and see if it makes any difference before I try more extensive ideas.
If it were here in my shop, I would pull the pan and one or two rod caps.....and the front and rear main cap.......if you see copper...then there you have it. This is a tough pill to swallow for some but about 50% of the time you can slip new babitts/bearing in and roll with it......it is really not that hard to do......can be done in a few hours.......be careful though because if you restore bearing clearances your oil pressure be too high with an HV pump......I don't use them on most anything.
Jebby
Is my vette stock?? HAHA
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From: Im not allowed to tell you
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all my chevies did that with a stock pump and 30 weight oil. The Winter number has no bearing on this issue, its a slinging property and not relevant to weight ....You should run an oil that has high ZDDP and zinc numbers and I would look for a 40 or 50 weight. I like Mobil 1 20W50 ITs High ZDDP and it fills in the worn bearing gaps/ worn oil rings in older engines and its pretty inexpensive at Walmart
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,809
From: Cool Northern Michigan
Mellings Pumps:
Std Vol std press
Std Vol HI press
HI Vol std press
Hi Vol HI press.
Pressure is determined by bearing clearance and what spring is installed in the side of the pump.
Volume is determined by bearing clearance, plus diameter of pickup tube, but mostly the sizing of the gears in the pump. H.V. gears are 25% wider.
Std Vol std press
Std Vol HI press
HI Vol std press
Hi Vol HI press.
Pressure is determined by bearing clearance and what spring is installed in the side of the pump.
Volume is determined by bearing clearance, plus diameter of pickup tube, but mostly the sizing of the gears in the pump. H.V. gears are 25% wider.