anyone know how to tell if compresion is lost this way

[nivlac]

my aa man opened my rad expasion bottle told me to crank the car over he looked in the bottle and said no compresion??!!!

i have never known this way of checking for compresion!! does anyone elese know if this works,

i am thinking it was friday afteernoon and he just wanted to get the car towed and get on with his day?

thanks for any information

 

[rallycinq]

If there are bubbles in the expansion tank then you could extrapolate that there is no compression because it ends up in the expansion tank, but i think the AA man was being a lazy wonker.

Cheers

D

 

[s130]

Sounds like the AA man is being a little vague with his statement / findings.

If there is compression leakage into the cylinder coolant jacket then compressed air will have to surface and escape somewhere. This will in most cases be via the coolant header tank.

However compression leakage could be passed damaged or missing pistons rings, burnt/bent valves or sometimes into an adjacent oil way (this is more rare).

If there was zero/no compression then no air could be forced into the waterways to appear in the header tank (or else where).

It is possible that the AA man was "dumbing down" his findings and really meant to say "there is a compression loss that appears to be into the colling system".

Generally speaking car engines with compression loss on one or two cylinders continue to run quite well but will be low on power/performance and possibly feel/sound a little lumpy. It is quit unusual for total loss of compression across all cylinders. When this happens then we are talking major engine damage.

 

[nivlac]

thanks for all your help guys