Anyone have an idea as to how much lower compression test numbers are on a cold engine vs. operating temp? I ask b/c the salvage yard tested the engine that I'm going to pickup, but they were cold numbers as the engine is already out of the vehicle. Luckily the numbers are all relatively consistent, but sounded just a tad low to me in the mid 150s.

 

In response to your question I would say that a hot engine would have a higher compression ratio due to the fact that hot metal expands but thats just my opinion.

 

did they do a wet test?

 

Nope, and for a $300 junkyard motor, I don't think they are going to go the hassle of doing it.

 

They also may not of had it up to specified RPM. Which is on a warm engine, fully charged battery, and good starter motor.