What should you do when a compression test reveals that compression is below average and the reason for a motor not working?
Low compression will not cause an engine to not run. It may not
run efficiently but it will run. Low compression on all cylinders
is caused by wear, and can only be fixed by overhauling the engine.
Low compression on just one cylinder can be a blown head gasket,
burnt valve, or a broken ring on that cylinder. I also depends on
what you mean by "below average". An engine with lots of miles may
very well have a compression reading that is below the factory
specifications and not be cause for alarm. It depends on how much
below specs that compression is. In any case, the only fix is to
open the engine up.