oil pressure

[Philip Graham]

Well guys I have another problem. I had my 350 rebuilt and It is running good. I only have about 100 miles on it so I have not been hard on it. I finally let the rpm get up to about 3000 and the oil pressure drops from about 60 lbs to 20. I let the rpm drop a little lower and it rises back up again. I have not tried another gauge yet or anything else. I thought I would get some ideas first. The gauge I am using is a mechantical gauge.

[Bob Parmenter]

Short answer given your description of increasing flow and pressure drops, then decreasing flow, rises again, you're probably dumping over the pressure relief. If you're running 60psi below 3000 when it's warm your oil is too thick. Could also be the filter dumping over it's relief. There are several variables so it could be other things, but those are the basics to start thinking from.

[Philip Graham]

Thank you Bob. I do not know much about these relief valves. Please can you tell me how to check them out?

[Bob Parmenter]

Okay, let's back up a step. Trouble shooting is about evaluating step by step, or a process of elimination. Deal with some basics first. Perhaps I should have emphasized the oil viscosity thing more.

What oil viscosity are you running?
Are the numbers you've shown above at cold or warm?
Have you checked the oil level?
Is it low or high, or just right?
Do you know if the proper dip stick was used at rebuild?

In a sense you can't "check" the pressure reliefs except by what you're already seeing. There's one at the oil pump and there's one in the filter (assuming you're using a good quality filter). While the symptoms are of pressure relieving (dropping), it could also be caused by oil starvation. Oil starvation could happen from too viscous of an oil, a partially plugged oil filter, contamination (blockage)of the oil pickup screen or other part of the oil circulation system, low oil level, or oil aeration of the oil (result of too full).

I'd like to ask if it's been doing this from the beginning, but you've indicated that you've not operated it much, and that you're operating differently now than before. Not much apples to apples there.

[Philip Graham]

The oil pressure is ok now. After I got home I knew that I had overfilled the oil maybe a quart. I thought well since I was going to change it after just a few miles it would not hurt anything. But after Bob said overfilling might be a problem I changed the oil again. After changing the oil I took the car for a spin the oil pressure was good about 40 pounds. Thank you all for your help!

[Bob Parmenter]

Phew!!