[DeTomaso] Compression test - hot or cold motor.

[JDeRyke at aol.com]

In a message dated 7/31/06 7:45:30 PM, mbefthomas at comcast.net writes:

<< Should I do a compression test with a warm or cold motor.  >>

MIke, I think it will make little difference whether the block is hot or 
cold. FWIW, the way I was taught to do this test is:
A- block the throttle wide open so as to not restrict the intake. Disconnect 
the coil low-tension wires or the hot wire to any electronic control box. NOT 
doing this can blow up the ignition box on some systems.
B- remove all spark plugs to even out the strain on the starter.
C- spin the engine 4 times so as to be certain you get a compression stroke 
in the mix.
All cylinders should test within +- 15 psi
Then, to any low-testing cylinders, add a spoonful of motor oil and re-do 
that cylinder as above. If the pressure comes up markedly, the rings are bad (at 
cranking speeds, oil will temporarily seal any leaks); if no change, one or 
more valves are bad as oil doesn't seal them up.
I now prefer to do a leak-down test since for the same amount of effort you 
can get much more information about the engine's condition. Good luck- J DeRyke