Oil Pressure
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
Oil Pressure
I have a 1976 L-48. When the car is cold the oil pressure is around 20psi at idle. When the car warms up it is very low...and doesn't seem to change based on RPM.
When I first noticed the problem I changed the oil and filter...no affect. I changed the sending unit...seems lower with a new unit. Do I need to take the pan off next to check the pump?
When I first noticed the problem I changed the oil and filter...no affect. I changed the sending unit...seems lower with a new unit. Do I need to take the pan off next to check the pump?
Intermediate
Joined: Feb 2012
Posts: 28
Likes: 0
I would buy a mechanical oil pressure gauge and rig it up for temporary use. You may find that the mechanical gauge shows that all is well. In that case you can relax and fix the problem with your existing gauge in the car. If the mechanical gauge verifies what you are seeing with the existing gauge, time to diagnose the engine.
Thread Starter
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
I forgot to mention that the sender attached to a brass fitting connected to the engine. Is it possible that the brass fitting could be cracked and causing a false reading?
I ask as many questions as possible before I put these old knees near the ground so I can crawl under a car
I ask as many questions as possible before I put these old knees near the ground so I can crawl under a car
Burning Brakes
Joined: Mar 2005
Posts: 1,231
Likes: 34
From: Ontario
I would put fresh 15w40 oil in and fully warm up the engine and then check it with a good mechanical gauge . On seccond thought I would install the gauge first before warming up the engine . You do not need a lot of pressure at idol , if you don't hear any knocking at idol you prob have enough pressue .
Back in the day I think the idiot light sensor would put on the light around 5 or 6 psi, GM had lower pressure switches that they would install if needed .
Bill
Back in the day I think the idiot light sensor would put on the light around 5 or 6 psi, GM had lower pressure switches that they would install if needed .
Bill
Drifting
Joined: Jan 2008
Posts: 1,517
Likes: 37
From: The Woodlands Texas
I too am confused.
My 72 stock engine has a constant pressure of aobut 25 PSI, regardless of any condition. The gauge shows 35 (straight up mark) as the target.
My 64 (highly moded engine) oil pressure is around 80 PSI under throttle, and about 60 at idle. The high pressure is driven by my oil pump, so I get that.
So what confuses me is the wide extreme vs what do you really need..... is 25 too low...is 80 too high?
My 72 stock engine has a constant pressure of aobut 25 PSI, regardless of any condition. The gauge shows 35 (straight up mark) as the target.
My 64 (highly moded engine) oil pressure is around 80 PSI under throttle, and about 60 at idle. The high pressure is driven by my oil pump, so I get that.
So what confuses me is the wide extreme vs what do you really need..... is 25 too low...is 80 too high?
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
You want about 10psi. per 1000rpm. On a small block there is a pressure port at the back of the block, on top, just behind the rear edge of the intake manifold and under the distributor. Normally a square headed 1/8 in. plug. Tap into this port with an inexpensive mechanical guage, one that uses a plastic tube and brass fittings. Tape the guage to the windshield with good old duct tape, down low, so you can see it from the drivers seat and take the car for a drive. This will give you an idea of where you are. You can just see the plug in this pic. mike...
Last edited by mds3013; Mar 24, 2012 at 09:42 AM.
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
80 psi is not "bad".....it's just not necessary. You may have installed a high volume oil pump or a pump with a high pressure regulator spring. For a racing engine, that would be a VERY good thing; for a street machine, it's not necessary.
A stock Chevy V8 engine will live just fine with 10-15 psi oil pressure at idle when warmed up. Usually, at cold startup with choke on, a stock oil pump will provide around 30 psi [or more]; and that will drop to about 20-25 when the choke drops out (engine & oil still cold).
If you measure oil pressure with a good mechanical 'alternate' gauge and it checks less than 10 psi at warm/idle, you may have some kind of internal leakage or wear problem (crank/cam bearing wear) that is allowing normal oil pressure to bleed off. In that case you might want to drop the oil pan and pull a couple of lower rod bearing caps to check the condition of the bearings. If you find no significant problem, you can also change the oil pump and/or regulator spring to bump-up the oil pressure a bit while the pan is off.
A stock Chevy V8 engine will live just fine with 10-15 psi oil pressure at idle when warmed up. Usually, at cold startup with choke on, a stock oil pump will provide around 30 psi [or more]; and that will drop to about 20-25 when the choke drops out (engine & oil still cold).
If you measure oil pressure with a good mechanical 'alternate' gauge and it checks less than 10 psi at warm/idle, you may have some kind of internal leakage or wear problem (crank/cam bearing wear) that is allowing normal oil pressure to bleed off. In that case you might want to drop the oil pan and pull a couple of lower rod bearing caps to check the condition of the bearings. If you find no significant problem, you can also change the oil pump and/or regulator spring to bump-up the oil pressure a bit while the pan is off.
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
if the spring were weak, it might allow the oil to bypass at a lower rate, there isnt usually any partial to it, other things that cause low oil pressure are a worn out pump, worn out bearings , plugged oil pump intake, and worn out oil or oil not spec'd for your engine. Like if you're running synthetic oil in an engine thats only had dino oil all its life, or if you just bought the car and the po was running 20/50 cause of a low oil issue and you put in 10/30 synthetic....just examples.
Intermediate
Joined: Mar 2012
Posts: 31
Likes: 0
From: Grand Island Nebraska
Mike, I am going to try your suggestion. In your photo it is obvious there are parts missing from your motor for me to reference where the square plug is located. I'm not real familiar with motors but would like to try this myself. Could you post another photo where the plug is. Thanks
Intermediate
Joined: Mar 2012
Posts: 31
Likes: 0
From: Grand Island Nebraska
You want about 10psi. per 1000rpm. On a small block there is a pressure port at the back of the block, on top, just behind the rear edge of the intake manifold and under the distributor. Normally a square headed 1/8 in. plug. Tap into this port with an inexpensive mechanical guage, one that uses a plastic tube and brass fittings. Tape the guage to the windshield with good old duct tape, down low, so you can see it from the drivers seat and take the car for a drive. This will give you an idea of where you are. You can just see the plug in this pic. mike...
Thanks!
Last edited by longnose624; Mar 26, 2012 at 11:48 AM.
Intermediate
Joined: Mar 2012
Posts: 31
Likes: 0
From: Grand Island Nebraska
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
The oil pressure port they're referring to is just to the left (driver's side) of the distributor, just behind the back edge of the intake manifold. It's a small hole and plug, only about a 1/4" in diameter.
Intermediate
Joined: Mar 2012
Posts: 31
Likes: 0
From: Grand Island Nebraska
Intermediate
Joined: Mar 2012
Posts: 31
Likes: 0
From: Grand Island Nebraska
I believe I located this port and with all the spark plug wires and other parts in the way I don't see how I would be able to screw a pressure gauge into the port without removing all these other parts first? Any ideas? Thanks
