LT1 oil pressure

[Paul K.]

what is normal oil pressure?

I have a 70 LT1 that is very original, Lately the oil pressure goes to 70 lbs . I checked with a different gauge, and the pressure showed 75 lbs.
after warm up at idle, it will drop to 45 plus, but goes right back up when when giving it some throttle.
What would cause this?

Oil is 10w 30 Joe gibbs driven oil
Would a motor flush help?


Paul Klemetson

[Mark F.]

Re: LT1 oil pressure

Paul,

❶ Dirty or gummed up oil filter ? Has it been changed recently ? If not, that's the easiest potential fix

❷ Blocked oil passages ? hopefully this is isn't it, that's why I'd try #1 1st

❸ Based on your 2^nd

[Duke W.]

Re: LT1 oil pressure

The original hot oil pressure spec is 55-60 psi at 2000 revs and above, and it should have an 80 psi oil pressure gage. The OE pump was the same as the lower performance engines (40-45 psi hot at 2000 and above), but has a stiffer relief spring.

GM has no hot idle oil pressure spec, but 30-35 psi is typical at about 900 RPM idle speed. Given that you report 45+ the engine probably has a "high volume" oil pump with a stiffer than OE relief spring.

Replacing the OE pump with a "high volume/high pressure" pump was a favorite revenue generator for so-called "engine builders" over the years, and it still happens today.

It won't do any harm other than increasing parasitic drag and heating up the oil. If you really can't stand it you'll have to drop the pan and replace the bubba pump with a standard volume pump and 55-60 psi spring, but even that is a crap shoot whether or not you will have an equivalent OE spring.

Last time I heard a few years ago both the OE standard pressure and high pressure spring were still available from GM.

Duke

[Duke W.]

Re: LT1 oil pressure

Paul,

❶ Dirty or gummed up oil filter ? Has it been changed recently ? If not, that's the easiest potential fix

❷ Blocked oil passages ? hopefully this is isn't it, that's why I'd try #1 1st

❸ Based on your 2^nd test w/ a separate gauge, it doesn’t appear it would be a faulty or failing oil pressure gauge…so, that can probably be eliminated as a potential problem.

Good luck !

A "dirty or gummed up oil filter" will REDUCE oil pressure, and if the filter offers more than 10 psi back pressure the oil filter relief valve will open.

It's about 99.99 percent probability that the "problem" is a "high pressure/high volume" oil pump replaced the OE pump sometime in the last 50 years.

Duke

[Mark E.]

Re: LT1 oil pressure

A "dirty or gummed up oil filter" will REDUCE oil pressure, and if the filter offers more than 10 psi back pressure the oil filter relief valve will open.

It's about 99.99 percent probability that the "problem" is a "high pressure/high volume" oil pump replaced the OE pump sometime in the last 50 years.

Duke

Paul,

Your post suggests no mechanical changes before oil pressure increased ("Lately the oil pressure goes to 70 lbs"). Is this so?

[Mark F.]

Re: LT1 oil pressure

A "dirty or gummed up oil filter" will REDUCE oil pressure, and if the filter offers more than 10 psi back pressure the oil filter relief valve will open....Duke

OK Duke,

I thought the filter element was on the positive pressure side of the oil pump...thus if dirty; higher pressure would be needed to pump it thru.

Based on what you are saying, the filter element must be on the negative pressure side...

[Paul K.]

Re: LT1 oil pressure

No mechanical changes other than a coolant and radiator hoses replaced
Paul Klemetson

[Duke W.]

Re: LT1 oil pressure

OK Duke,

I thought the filter element was on the positive pressure side of the oil pump...thus if dirty; higher pressure would be needed to pump it thru.

Based on what you are saying, the filter element must be on the negative pressure side...

Everything past the pump gears is positive, but like I said, if the filter gets plugged up and the pressure drop across it is more than about 10 psi the bypass valve opens up so the oil galleries see full pressure, but the oil is not filtered.

Duke

[Mark E.]

Re: LT1 oil pressure

No mechanical changes other than a coolant and radiator hoses replaced
Paul Klemetson

This is curious. What was oil pressure before this phenomenon?

With no mechanical changes and assuming it's the same oil, there's no obvious reason for an increase in oil pressure. A failing oil pressure relief spring?

In any case I don't recommend an engine flush. That risks bearing and valve train damage.

[Erich M.]

Re: LT1 oil pressure

Paul,

LT1 came with a high performance oil pump. It is not the same as other small blocks. My pressure is above 70 psi on start up at 2800-3200 rpm. Pressure drops to about 35-40 psi after warm up at 900 rpm using 5W-30 synthetic oil. Sometimes if the car sits for a longer period of time before start up it takes 10-15 minutes before the pressure drops to 35-40 psi even if the rpm is off fast idle.

I have had no oil pressure problems with my car and the pressure will be above the 35-40 psi range if the rpm is above idle (I think around 60 psi depending on the rpm). If you like, I can give you more specific rpm-pressure data the next time I run my car.

Erich Meyer
72 LT1, original owner - 5 Star Bowtie & Top Flight

[Duke W.]

Re: LT1 oil pressure

The only difference between the base engine oil pump and the LT-1 oil pump is the pressure relief spring.

GM only specifies HOT oil pressure at 2000 RPM, which is listed in the AMA specs, and I quoted it in post #3. GM does not spec hot idle oil pressure, and it's highly dependent on idle speed, So a base engine idling at 500 will show lower pressure than a mechanical lifter engine at 900.

Duke

[Paul K.]

Re: LT1 oil pressure

Thanks for all the great info, I think my oi pressure is fine]
Paul Klemetson

[Dan A.]

Re: LT1 oil pressure

Paul,

I am running 10w-30 VR1 in my 72 LT-1 and the oil pressure runs exactly like you and Erich describe, and has for the 9 years I have owned it.

[Erich M.]

Re: LT1 oil pressure

Duke,

Somewhere during my many years of owning the car I thought I had read that the LT1 came with a high volume oil pump, but I can't find that documentation at this time. Please advise what the "AMA specs" are and where I can find them.

Erich Meyer
72 LT1, original owner - 5 Star Bowtie & Top Flight

[Duke W.]

Re: LT1 oil pressure

The AMA specs are included in the "vehicle information package" you can download from www.gmheritage.com. Click on "resources" and follow the links to your year Corvette or any other GM car.

Duke