Low Oil Pressure

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Nelson7604

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I have a 318 (I believe it's a 71) that I just rebuilt. I primed the oil pump with a cordless drill and I got 60psi cold. I broke in the new cam yesterday and noticed that I had 20psi oil pressure(two different gauges). I diagnosed this as the thin 10-30W break in oil. I drained the oil, changed the filter and fired it up again on straight 50W. No change in oil pressure: 20psi at 950-1000 rpm. Is this ok? If not what could the problem be? Thanks
 
you need 10 psi for every 1000 rpm....does the oil pressure go up with the rpm.?
 
That's not too bad for idle, but what are you getting at 2000 and up warm?
 
20 psi is good. the light starts to flicker at like 7. 10 per K is a good rule to shoot for. If you get 20 psi at 4-5000 rpm, then you got a stuck (open) bypass valve in the pump. Pull the cotter pin and plug and check spring. Install 340 spring while you are at it.
 
pishta said:
20 psi is good. the light starts to flicker at like 7. 10 per K is a good rule to shoot for. If you get 20 psi at 4-5000 rpm, then you got a stuck (open) bypass valve in the pump. Pull the cotter pin and plug and check spring. Install 340 spring while you are at it.
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We just found out this week that the Mellings oil pumps come with the high pressure spring, both standard and high volume. No need to change the spring in those if you are running them....
 
Thanks for the quick responses. I haven't checked if the pressure moves with the rpm. Been afraid to fire it up again. With the break in oil I was getting around 40 when it first fired at 2000-2500.
 
Nelson7604 said:
Thanks for the quick responses. I haven't checked if the pressure moves with the rpm. Been afraid to fire it up again. With the break in oil I was getting around 40 when it first fired at 2000-2500.
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listen to yourself, with the THINNER oil you get 40 at 2500, with the thicker oil you get 20 at 1000
if we want to see 10 PSI per 1000 RPM over idle then you should see 35 PSI at 2500 and you are 5 PSI over that

seems to me that you are good to go
 
If it has 5 PSI at 900 RPM that is acceptable. I don't know of any service manual that gives a spec at idle. All I have ever seen gives the spec at 2000 RPM or so. You need to think in perspective. Your 20 PSI means 20 pounds per square inch. Per square inch of what? The oiling system of course. So lets say your oiling system is 5 square inches for the sake of easy math. At your 20 PSI at idle, that's 100 pounds of oil pressure.

You need to keep in mind, gauges are an approximation at best. Variances in everything from the printed face, to the needle, and the actual mechanism. This is why the spec is given at a higher RPM. Because at idle, the accuracy is just not there. I have always said if the needle is OFF ZERO at idle, but has good pressure above ide, it's all good.
 
FSM
ENGINE "318" 340" "360"
ENGINE LUBRICATION
Minimum Pump Pressure @ Idle 8 ps¡
Operating Pressure at 2000 Engine RPM 30—80 lbs.
 
I took the manifold off and found that I had missed an oil galley plug. Pressure was bleeding off into the valley. I plugged it and the pressure hasn't dropped below 60 since. Problem solved.
 
Glad to hear that
even though you were still running sufficient oil presure I'm sure this feels a lot better
 
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