Oil Pressure Reading

[O Vette]

Could someone give me an opinion, please? I was looking at a 1975 with 63K on it and noticed that after car was running for about 4-5 minutes the oil pressure gage was reading a bit below 40. It was a nice warm day. The car recently had a new oil pump installed. Is that pressure level something to be concerned about and could the lower reading have anything to do with the new oil pump (not installed correctly). Could the new oil pump have been installed to increase an even lower prior reading? I've read through some posts on this subject and I realize this could be a stickler of a problem with many causes. I guess my main questions are - is oil pressure that reads a bit below 40 okay and what would be the symptoms that would cause you to replace an oil pump? Thanks for your help.

 

[TimAT]

They could have installed the pump to cover a number of things. Worn bearings would be top on the list. At idle, just under 40 psi is not a real issue. I run over 40 at idle and 60-70 at 5000 RPM, but with the pump I have it's expected.

 

[spikebot 81]

I just finished a new engine install with a stock gm oil pump for sbc. 10w 30 oil. On cold start about 50 psi after engine is hot at idle 38 to 40 psi

 

[Vettehead Mikey]

Might help to know the range of indicated oil pressures- what is it at cold idle, hot idle, highway speed etc etc. When you say running after 4-5 minutes with 40 psi- is that at idle or at highway speed?

 

[O Vette]

Might help to know the range of indicated oil pressures- what is it at cold idle, hot idle, highway speed etc etc. When you say running after 4-5 minutes with 40 psi- is that at idle or at highway speed?

Thanks for the replies. That 4-5 minutes was idling. At 63K miles, I am wondering if the engine has another 10 or 15 thousand miles in it or if it would need a rebuild soon. Would a bad oil pump result in low oil pressure? Maybe that is why it was replaced. I'm interested it purchasing the car for local cruise ins not as a daily driver.

 

[Vettehead Mikey]

40 psi at idle is excellent, bordering on 'high'. Usually the original engine is good for at least 100K miles on it's first life, sometimes 150K or more.

 

[Hib Halverson]

Could someone give me an opinion, please? I was looking at a 1975 with 63K on it and noticed that after car was running for about 4-5 minutes the oil pressure gage was reading a bit below 40. It was a nice warm day. The car recently had a new oil pump installed. Is that pressure level something to be concerned about and could the lower reading have anything to do with the new oil pump (not installed correctly). Could the new oil pump have been installed to increase an even lower prior reading? I've read through some posts on this subject and I realize this could be a stickler of a problem with many causes. I guess my main questions are - is oil pressure that reads a bit below 40 okay and what would be the symptoms that would cause you to replace an oil pump? Thanks for your help.

Indicated oil pressure depends on a number of factors. Some are:

1) Gauge condition
2) Engine condition
3) Oil pump pressure relief valve value

Without knowing more about the engine and guessing that this 75 has a base small block in it and guessing that it ran for 4-5 minutes at idle and you were reading the gauge while the engine was at idle...I'd say 40 psi is just fine.

 

[O Vette]

Thanks again for the informaton. Hib, your assumptions were right on the mark. Makes me more comfortable in pursuing the Corvette. The original owner has it up for sale and it is all original except for new SS brakes & rotors, radiator, hoses and belts. Exhaust looks stock. Original paint with cracked bumpers and there a some paint chips on the doors. The owner (not mechanically inclined) has taken it to the same mechanic every year for the last 37 years for an annual check up. Everything works but, it needs a new leaf spring. The owner bought it off the lot and it is a base model L48 with no power locks, windows or AC. Wish it had a bit more HP but, 1975 was the low point for C3's. I'll use the car for pleasure driving on a limited basis so the lack of "umph" is really not a concern. It is kind of nice to find a pretty much original Vette that has not been messed with.

 

[Hib Halverson]

If the car has a base engine, it is likely, the oil pump had the standard pressure relief valve spring in it which usually produced about 40 psi oil pressure.

 

[O Vette]

Thay you for your help. I'm pretty much a novice and trying to learn what I can. This forum is valuable to me. I know C3's are old Vettes and will need repairs but, their looks are just beautiful to me. i believe, if they started making them again tomorrow, they would sell. The styling is still way too cool.