low oil pressure
Thread Starter
Burning Brakes
Joined: Dec 2003
Posts: 1,149
Likes: 153
low oil pressure
Can anybody help out with some information on a problem I'm having?I gave my engine builder the parts from my 427 and he honed and assembled the short block with new bearings,rings and timing chain.Now when the car idles it has about 10lbs. oil pressure when hot 36lbs when cold.My old engine had 35lbs at idle when hot going to about 60lbs when driving.This one onlygoes to 36lbs when driving.It;s a stock oil pump and I'm using 30 straight weight oil for break in.I'm a believer in high oil pressure at an idle,right or wrong.pressure goes down rather fast when coming to a stop.Aside from bad bearing clearances I don't know what would cause this.I'll be going back to him in a week or so but would like some suggestions so I can be a little more knowegible when I speak to him. thank you.
Le Mans Master
Joined: Feb 2000
Posts: 7,032
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From: Newburgh NY
Assuming everything is sealed properly and the correct bearings were used, then my .02 would be the motor is not clearanced correctly. It doesn't take too much extra tolerance to affect oil pressure. Unfortunately it's not an easy fix.
I just had a similar situation with a C5. I had to pop the motor out a second time and bring it back to the shop because of pressure. It's a long story but the crank had to be turned and new oversize bearings to set it up correctly. Should have been done the first time.
I just had a similar situation with a C5. I had to pop the motor out a second time and bring it back to the shop because of pressure. It's a long story but the crank had to be turned and new oversize bearings to set it up correctly. Should have been done the first time.
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I have the original 427/390 in my 68. Fresh rebuild to stock specs with a standard oil pump. I am running Rotella 15/40. At idle, warm my pressure is between 15-20. Cruising on the highway at 70 it is about 40. The car runs extremely strong and uses no oil. I have had other big blocks that run in this same range with no problems. If the car is running well I would view this as a non issue.
Team Owner
Joined: Jun 2001
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From: Virginia USA
The rule of thumb I've always used is 10psi per 1000 rpm on the older style Chevy engines. Keep in mind I am a SB guy so I don't know if this is true for BB's. My 350 runs around 15psi at idle hot and around 50 at highway speeds hot.
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Well, it sounds like it's a little loose on bearing clearances. Did you add any of the lifters with an EDM hole for the cam (solid flat tappet) or rollers with pressurized oiling to the axles? There are lotsof places to *leak* in a motor. Could be lifter to bore clearance, cam bearings, etc. It all adds up. I've seen a pump that didn't seat all the way down on the main cap due to hitting a main cap stud/nut.
If all else is good, a HV pump will help. The clearances are what they are unless you tear it all down again. Did he give you the clearances he set the mains and rods to? Was crank turned or polished? A little loose is better than a little tight. I also always take the pump apart and tighten the end play my sanding the housing to get .0005-.001 to help out. Usually they are .002-.0025..but I've seen some out to .0045.
You may also end up being best with 20/50 oil.
Have you double checked with another gauge to be sure? Seems strange that cold idle and cruise are both exactly 36 psi?
I'm with you, I like lots of oil pressure. Engines will live without much....but I like the insurance. When summer comes and it gets warm outside, the pressure is just going to get less and less.
JIM
If all else is good, a HV pump will help. The clearances are what they are unless you tear it all down again. Did he give you the clearances he set the mains and rods to? Was crank turned or polished? A little loose is better than a little tight. I also always take the pump apart and tighten the end play my sanding the housing to get .0005-.001 to help out. Usually they are .002-.0025..but I've seen some out to .0045.
You may also end up being best with 20/50 oil.
Have you double checked with another gauge to be sure? Seems strange that cold idle and cruise are both exactly 36 psi?
I'm with you, I like lots of oil pressure. Engines will live without much....but I like the insurance. When summer comes and it gets warm outside, the pressure is just going to get less and less.
JIM
Team Owner
Joined: Jan 2006
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From: Crossville TN
Stick an accurate oil pressure gauge in your pressure circuit to compare with your gauge. It might be that your gauge just reads a bit low. 10-20 psi at idle is not bad (for a stock pump). If you feel that is not enough, you can always change out the pump regulator spring and bump it up a bit. There should be no need for more than 20 psi at idle, unless you have high-lift cam, stiff valve springs and flat-tappet solid lifters.
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