My Chilton manual say to do a compression test you warm the engine to normal operating tempurature. Then disable the ignition system & disconnect all spark plugs. How am i to remove spark plugs from a car that is this hot? I think they must be talking about an engine out of the car. What is the right way?

 

I've been doing compression tests on my cold engine on and off for a month. If you want a REALLY accurate comparison of all the cylinders then yah, go ahead and try to do it warm (good luck). But if you are just trying to make sure the engine is in relatively good health a cold compression test is fine. The thing that seems to have made the biggest difference in my compression tests (other than a warped intake valve) was how much juice the battery had in it. If you crank it over too many times or have a low battery the engine will crank much slower and give you a much lower reading. That's my two cents anyway.

-Gabriel

 

I beleive that it is fine to do a compression test without your motor warmed up. At the least it'll give you a basic idea of what the compression is.

 

The ideal is a warm engine as this lets the pistons and rings expand to provide the best sealing. I believe a cold compression test is fine as I'm looking for variance between the 8 cylinders.

 

Warm is how it is done, but if you can't, do it cold.