L79 oil pressure question

[Chris E.]

What kind of oil pressure are you guys seeing on your L79 motors? I spoke with my engine builder and he said that on a newly built motor like mine, the initial pressure could be as high as 60, then idling down to 30-40. But, it'll "run higher than stock".

Thoughts?

[Jack H.]

Re: L79 oil pressure question

There are quite a few variables involved in the answer to this question. The VERY rough design approximation is 10 lbs/1000 RPM which is why the high reving engines often had 80 lb oil pressure gauges.

BUT, on freshly rebuilt engines, internal clearances are typically very tight until the engine has completed break in. During that period, you CAN expect to see elevated oil pressure readings.

Also, engine hot vs. cold makes a difference as well as the characteristics of the oil you're using. It's most common today to run multi-weight oils where you can expect to see pressure difference(s) compared to the factory original single weight oils (change according to the season) most of these cars came from the factory with.

Last, you have the issue of the specific characteristics of the oil pump (standard, high flow, Etc.). So, trying to lay down a set of numbers that are 'typical' is tough. But, in general, your engine builder is right...

Expect higher than normal pressure readings from first fire through break-in.

[Doug F.]

Re: L79 oil pressure question

your engine guy sounds like he knows his stuff, thank goodness he did not put in a high pressure pump, no good can come from that,

[Duke W.]

Re: L79 oil pressure question

What kind of oil pressure are you guys seeing on your L79 motors? I spoke with my engine builder and he said that on a newly built motor like mine, the initial pressure could be as high as 60, then idling down to 30-40. But, it'll "run higher than stock".

Thoughts?

The AMA specs list the hot oil pressure of your engine at a specific RPM, and it's probaby in the range of 30-45 psi. GM never specified cold start-up or hot idle oil pressures, but cold start-up oil pressure is typically higher than normal hot oil pressure.

Duke

[Chris E.]

Re: L79 oil pressure question

your engine guy sounds like he knows his stuff, thank goodness he did not put in a high pressure pump, no good can come from that,

He did put in a high pressure, regular volume pump. Can you expand on your comment? The motor hasn't been started yet.

[John H.]

Re: L79 oil pressure question

He did put in a high pressure, regular volume pump. Can you expand on your comment? The motor hasn't been started yet.

There's no need for the "high-pressure" pump - the standard one will work just fine. All you need to do is to change the relief spring in the pump cover to the standard spring.

[Gary G.]

Re: L79 oil pressure question

I think Chris's question is will there be any long term issues with staying with a HP pump. My L79 was also rebuilt several years ago with a HP pump and so far, so good. Should we be concerned?

[Chris E.]

Re: L79 oil pressure question

I think Chris's question is will there be any long term issues with staying with a HP pump. My L79 was also rebuilt several years ago with a HP pump and so far, so good. Should we be concerned?

Yes, that is my question. The engine shop I used normally builds race motors. They're used to building things for ultimate reliability.

Do I need to have them change that spring on the oil pump? Am I going to hurt the long term reliability of the engine?

KEEP IN MIND, this is THE original motor that came with the car. The car is family owned since 1973, I have the tank sticker, the POP and a hand written mileage log. I ABSOLUTELY do not want to have a problem with the motor. Seems to me that more oil vs. less oil is a good thing........I don't know a lot about motors though.

[Duke W.]

Re: L79 oil pressure question

GM used a 55-60 psi relief spring on mechanical lifter SBs beginning in late '63, but used the standard 30-45 psi spring in all other SBs including L-79.

Higher than necessary pressure costs some power and fuel economy, plus if you have a 60 psi gage, it will be pegged most of the time.

My '63 L-76 has the standard pressure spring, and I never had any oil system problems, including race track hot lapping.

Yeah, all these "engine builders" build "racing engines" and they want to install "racing stuff" in road engines. It's absolutely unnecessary! GM knew what they were doing.

Since the engine is not yet in the car, it's easy to remove the pan and change to the correct OE relief spring.

Duke

[Chris E.]

Re: L79 oil pressure question

Ok, so it sounds like there is NOT any reliability issue for either the standard pressure or the high pressure relief spring.

It also sounds like I have two choices.

1. Replace the high pressure spring with a regular pressure one and be done.
2. Leave the spring alone and recalibrate the oil pressure gauge so it reads within a normal range, knowing that it reads 10 pounds low all the time (for example).

[Duke W.]

Re: L79 oil pressure question

Change the spring. Don't Micky Mouse the oil pressure gage.

Duke

[Paul D.]

Re: L79 oil pressure question

My 1967 L79 runs 30-35 hot idle,45-50 at 2000rpm with a std oil pump on a fresh rebuild using 10-30wt GTX oil. It always ran same pressures even before rebuild. It passed PV with no problems............

[Mike M.]

Re: L79 oil pressure question

Also if you plan on PVing your car at some point you will have to change the spring as the higher oil pressure will cause the car to fail.