Posted by daveyKin Pa [108.36.129.188] on Thursday, February 26, 2015 at 08:34:02 :
In Reply to: Re: Did a Compression Test Hot and Cold? posted by Willy-N [72.171.192.119] on Wednesday, February 25, 2015 at 22:51:19 :
Hi Willy,
The compression and vacuum readings will be lower the higher in elevation you go.
I am about 500' above sea level and normal vacuum is around 18"hg on most engines.
The accuracy in the test results is the constant methods & conditions of the testing.
If you have, lets say, a weak battery that the cranking RPMs are 25 or 50 RPMs slower for the last cylinder the compression will also be lower for that cylinder. Engine temps also affect the results. A warm engine has the metals expanded making all the internal clearances tighter which should increase compression.
HTH
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