Oil pressure Question
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Oil pressure Question
My 350 72 LT-1 engine runs at 35 psi while driving.However at idle the pressure drops to around 10 to 15 psi.Is this to low? engine burns no oil no leaks.Am running 20-50 castrol with ac filter.Would a new pump with a high pressure spring help? 
Pro
Joined: Apr 2004
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From: Atascadero Ca
low oil pressure = motor starting to go. If you have access to another gauge try hooking it up to the motor and make sure the one in the car is accurate. Using thicker oil or changing the oil pump alone would only mask the problem. Sounds like a rebuild is in your future. I'd verify with another guage then explore rebuild/replacement options. How many miles on the motor?
Melting Slicks
Joined: Feb 2000
Posts: 3,052
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From: Vancouver BC, Canada
Originally Posted by memLT-1
My 350 72 LT-1 engine runs at 35 psi while driving.However at idle the pressure drops to around 10 to 15 psi.Is this to low? engine burns no oil no leaks.Am running 20-50 castrol with ac filter.Would a new pump with a high pressure spring help?
-either the pump is not moving enough oil
-or the clearances in your engine are on the loose side
with that viscosity, your pressure are on low side, but not dangerous at all.
My BB was similar, so installed a new pump. beforehand, i tweaked the clearance between the gears and the cover to .0025". I also lapped smooth the cover face and used a tiny bit of sealant to ensure all the oil was actually going to the engine. my old pump had .006-7" clearance. New pump makes ~25 psi at idle. Old pump was 10 psi.
Melting Slicks
Joined: May 2003
Posts: 2,253
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From: Rochester Kent
Originally Posted by Turbo-Jet
Low pressure does NOT mean the motor is about to go...
-either the pump is not moving enough oil
-or the clearances in your engine are on the loose side
with that viscosity, your pressure are on low side, but not dangerous at all.
My BB was similar, so installed a new pump. beforehand, i tweaked the clearance between the gears and the cover to .0025". I also lapped smooth the cover face and used a tiny bit of sealant to ensure all the oil was actually going to the engine. my old pump had .006-7" clearance. New pump makes ~25 psi at idle. Old pump was 10 psi.
-either the pump is not moving enough oil
-or the clearances in your engine are on the loose side
with that viscosity, your pressure are on low side, but not dangerous at all.
My BB was similar, so installed a new pump. beforehand, i tweaked the clearance between the gears and the cover to .0025". I also lapped smooth the cover face and used a tiny bit of sealant to ensure all the oil was actually going to the engine. my old pump had .006-7" clearance. New pump makes ~25 psi at idle. Old pump was 10 psi.
It doesn't have to mean a terminal problem 
Instructor
Joined: Feb 2005
Posts: 147
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Hi: Just want to add one more thing to this thread. U can safely run a small block chevy on 5 lbs of pressure at idle. As long as the guage tends to move as you increase rpm. I agree with the others, check your guage first. Pump could be weak......but my guess is that your mains are gaining a little too much clearence. Goes with wear on the engine & high milage.
Instructor
Joined: Dec 2003
Posts: 129
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From: Rio Medina Texas
I have a question for those of you in this thread. Not on my vette, but on my chevy truck. It's a 93 PU with 5.7L TBI engine. I too had low oil pressure so suspected clearance issues, etc... I pulled the motor rebuilt installed hv pump and the pressure is better but still low (~10 lbs at idle). The gauge does move with RPM and I checked with mechanical gauge so I know it's real. I suspect the oil is not being forced to the galley by going around something but not familiar with possibilities. Any ideas? Thanks
Mark
Mark
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Joined: Dec 2000
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From: CO
There is another oil pump thread here and though this was on topic for this thread:
http://www.melling.com/support/bulletins/view.asp?id=5
I HAVE LOW OIL PRESSURE SO I'LL PUT IN A HIGH PRESSURE PUMP.The low pressure is usually caused by a leak or excessive wear in the engine. If the original pump has a 50 psi bypass and the engine will not get over 30 psi, then putting in a pump with a 75 psi bypass will not change a thing. You will still have 30 psi. You have to fix the leak or rebuild the engine.
SAME AS #3 EXCEPT I'LL PUT IN A HIGH VOLUME PUMP. The high volume pump does increase the flow so you will have some increase in pressure. However, you still have the original problem of a leak or worn out. The high volume pump just delays fixing the real problem. High volume pumps are for increased demands on the oil system such as higher RPM usage, racing, remote filters and or coolers, etc.
Oil pumps do wear out though, and they don't mention it. Or the relief valve could be stuck open or something.
http://www.melling.com/support/bulletins/view.asp?id=5
I HAVE LOW OIL PRESSURE SO I'LL PUT IN A HIGH PRESSURE PUMP.The low pressure is usually caused by a leak or excessive wear in the engine. If the original pump has a 50 psi bypass and the engine will not get over 30 psi, then putting in a pump with a 75 psi bypass will not change a thing. You will still have 30 psi. You have to fix the leak or rebuild the engine.
SAME AS #3 EXCEPT I'LL PUT IN A HIGH VOLUME PUMP. The high volume pump does increase the flow so you will have some increase in pressure. However, you still have the original problem of a leak or worn out. The high volume pump just delays fixing the real problem. High volume pumps are for increased demands on the oil system such as higher RPM usage, racing, remote filters and or coolers, etc.
Oil pumps do wear out though, and they don't mention it. Or the relief valve could be stuck open or something.
Last edited by flood; Mar 1, 2005 at 11:43 AM.
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Instructor
Joined: Dec 2003
Posts: 129
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From: Rio Medina Texas
I HAVE LOW OIL PRESSURE SO I'LL PUT IN A HIGH PRESSURE PUMP.The low pressure is usually caused by a leak or excessive wear in the engine. If the original pump has a 50 psi bypass and the engine will not get over 30 psi, then putting in a pump with a 75 psi bypass will not change a thing. You will still have 30 psi. You have to fix the leak or rebuild the engine.
but outside from bearing clearance what are some other possibilties for "leaks"?
Mark
but outside from bearing clearance what are some other possibilties for "leaks"?
Mark
Race Director
Joined: Dec 2000
Posts: 10,896
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From: CO
Originally Posted by soggybottomboy
but outside from bearing clearance what are some other possibilties for "leaks"?
Mark
The pressure relief valve could be stuck open on the pump.
An air leak (usually where the screen assembly is mounted to the pump). Check for loose connections, cracks, or holes. Since air is compressible, any air inside the oiling system can cause a fluctuation of pressure.
Too much oil in the crankcase (leading to air in the oil)
Excessive clearances within the engine (rod and main hearings, corn bearings, seals and oil plugs).
Oil leaking post the mounting pad area (usually caused by tightening the mounting bolts wrong).
Last edited by flood; Mar 1, 2005 at 11:55 AM.
Race Director
Joined: Oct 2000
Posts: 15,013
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From: central FL, near the beach.
Originally Posted by flood
The pressure relief valve could be stuck open on the pump.
An air leak (usually where the screen assembly is mounted to the pump). Check for loose connections, cracks, or holes. Since air is compressible, any air inside the oiling system can cause a fluctuation of pressure.
Too much oil in the crankcase (leading to air in the oil)
Excessive clearances within the engine (rod and main hearings, corn bearings, seals and oil plugs).
Oil leaking post the mounting pad area (usually caused by tightening the mounting bolts wrong).
An air leak (usually where the screen assembly is mounted to the pump). Check for loose connections, cracks, or holes. Since air is compressible, any air inside the oiling system can cause a fluctuation of pressure.
Too much oil in the crankcase (leading to air in the oil)
Excessive clearances within the engine (rod and main hearings, corn bearings, seals and oil plugs).
Oil leaking post the mounting pad area (usually caused by tightening the mounting bolts wrong).
soggy
loose lifter bores would kill psi
and u might try a distributor with an o-ring seal, stock has no seal and it could leak like crazy inside
sometimes frenzied rebuilders leave out the plug, under the rear main
Instructor
Joined: Feb 2005
Posts: 147
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Hi: I have to disagree somewhat about bearings, especially the mains, not being responsible for a drop in oil pressure. I had a SBC 350 have a drop in oil pressure & then I got that dreadful knocking sound at idle. Tore the engine down & discovered that the mains, especailly the forward ones, were bad, The main closest to the front was worn to the point that it was so thin in the middle, that it actually broke in half. Everything else in the engine looked good, including the lifter bores. All I did to the engine was re-grind the crank & added all new bearings (main & rods). Put the motor back together & when I got it running, the pressure read 35-40lbs at idle & it would jump to 60-65lbs as I went through the gears. The car was at normal operating temperature. When the engine was cold, it would bury the guage. I was using an LT-1 pump in the pan.
I agree that lifter bores can cause a drop in pressure, but you'd hear "noise" in the valve train long before you'd see the drop.
I agree that lifter bores can cause a drop in pressure, but you'd hear "noise" in the valve train long before you'd see the drop.
