Buick V6 Compression

I am looking at another (like I need more than the 3 I have) 225..... The owner says the long block has about 100 hrs. on it. He also states his mechanic ran a compression test on it. He said it has a solid 110 psi in all cylinders. I do not know if that was hot or cold, wet or dry or if they had the throttle open....My question is.......Do you think that if it was cold and dry with the carb closed would this be a good or bad number ? Thanks...

 

If you're at sea level that's kinda low. However, the most important thing is that they're all even.
If the test was done dry, and the throttle was closed, it might not be too bad.

 

Call me paranoid, but I haven't ever seen anyone post the same compression for every cylinder. I would question him a little closer on the the accuracy/honesty of the compression.

 

Good point-it's unlikely that all 6 are exactly the same.
Maybe take a battery & compression tester, and check it yourself?

 

Personally I don't use the compression test very often..........Although in most cases a variance of 10% +/- is within reason if you don't crank over the motor the exact same number of times and at the same speed the test is not accurate. Furthermore once the test is complete and you do have a low cylinder you still have no Idea really what the problem Is.

Compression tests are referred to as a cylinder moving or dynamic test while the Leakdown Test is a static or engine at rest test. Basically the Compression test tells you about your engines ability to generate cylinder pressure and a Leakdown Test tells you about its ability to hold pressure.

I like to use a Cylinder Leakdown Test:

This method requires a compressor whereby your injecting about 90 PSI into the cylinder at TDC. Both should be done on a warm engine but the difference in the leakdown test is that it will read the percentage of leak and by carefully listening you can tell where the problem is: Whistling air out of the intake track=Intake valve , same out of the exhaust=exhaust valve, take a breather off the valve cover and if air is escaping = rings or cylinder walls , Air bubbles in the collant = head gasket or a crack in the block or head, Air in the adjacent cylinder from the test= a head gasket leaking between the cylinders.

Lots of things to look at.........

 

Unless that is a 7.4:1 cali version, 110 psi seems really low for a 9:1 engine which should likely be at least 130 psi.

 

Thanks for the responses....I am going to try to get more information....

 

awesome insight tarry!
thats alot to consider and itll deffinately tell you exactly where the issue lies with each cylinder. i dig it.
its going in my book of tips and tricks!