Compression: engine cold vs engine hot

[Saville]

What, if any, difference can there be between compressions you measure when the engine is cold vs when the engine is hot?

Should they be identical? Close?

thanks

[vic syracuse]

Usually, but not always, they will be higher when hot. But a good engine should test OK when it is cold. I typically see compressions in the 70's on cold engines all the time, and never retest hot unless one is really different or substantially lower, such as in the 60's.

Vic

[Saville]

Originally Posted by vic syracuse

Usually, but not always, they will be higher when hot. But a good engine should test OK when it is cold. I typically see compressions in the 70's on cold engines all the time, and never retest hot unless one is really different or substantially lower, such as in the 60's.

Vic

Hi Vic,

In the airplane I'm considering, the owner says the compression is in the 60's when cold but mid 70's when hot. Exactly like your scenario above.

What does this mean? Is that a cause for concern?

thanks!

[vic syracuse]

With a gap like that it may not be a cause for concern IF you check the following:

Do the compression tests and see where it is leaking (rings or valves)
Is th eaircraft on an oil analysis?
How much oil is it burning. Burning NO oil is bad for aircraft engines. They are meant to burn some oil.
Be sure to check screen and cut open the oil filter.
If possible, download the engine data from the EMS and check for operating temps.

Call if I can be of help.

Vic
404-307-5133