Possibly low compression

[Thomas Yarri]

Hey guys, my engine only has 21,784 miles and is completely original. I had a shop check the compression and they said it was good at 150 psi on all cylinders. I read my Cadillac shop manual and it says 165-185 psi. Just wondering if maybe the rings are gummed up or if any of you could lend some advice. I thought about using BG epr to flush the engine and see if it comes up. Any advice would be greatly appreciated.

[Kevin Campbell]

A lack of use wouldn't be helping.

Stuff a tank of premium fuel in it and start driving.

I wouldn't be getting too worried about the whole thing though.

[Thomas Yarri]

I’ve put 1200 miles on it and only running premium. I suppose I’ll just keep driving and enjoying. But I don’t want to damage it. For a car that only averaged 357 miles per year until I got her, 1200 miles is a lot lol

[Jason Edge]

I agree with Kevin, 150 is not that bad, and consider 140 to 160 pretty decent. You generally only see 165 to 185 on new or rebuilt engines. The bigger issues that can point to a problem like blown head gasket broken valve springs etc, is when you have big difference between pistons, or a piston and the rest of them. Seems yours are all consistent and should be good to go. Not saying to go put thousands of miles on the engine, but expect some running/driving may bring it up a tad.. and the oil pressure.

[Thomas Yarri]

Thank you Jason, that definitely makes me feel better. I’m currently having all the gaskets replaced, carb rebuild and new hoses and original radiator repaired. I didn’t want to spend that kind of money to have a huge failure. I hope to be able to take some long rides in her soon. 

[Tony and Ginny 429]

 Thomas

I would be adding the correct amount of  marvelous mystery  oil to the gasoline every 2-3 tanks   for a while 

The oil should increase compression some and lube the rings to free them if they need that as it oils the top of the cylinders and valve stems and gets into places stock oil cannot as it is a  much thinner oil 

The fact that your compression numbers are similar in all 8 cylinders is a good thing 

I am a fan of MM oil ( to the gas ) and STP ( to the crankcase in conventional oil ) for over 60 years —but  it is not for those who are  non believers and need to call it snake oil 

Your car - your call 

Enjoy 

[Tony and Ginny 429]

Rislone makes a product that is added to the engine oil to free up lifters and rings with —-a new oil change that may help improve your rings condition if your ring need that 

There produces are around for 100 years 

I am currently using Castrol GTX 10-30 conventional motor oil with the Rislone  ZDDP zinc additive to meet my flat tappet cam and engines oil needs at the correct viscosity for the engine 

I do think your engine is suffering from non use possibly to some degree 

My other thought would be — was the compression test done correctly ? 

Enjoy 

[Thomas Yarri]

Thank you for the advice I will try some of these out and see how it does.