Leak Down test and oil use...again

John Gourley azaudi at msn.com
Wed May 19 01:25:03 EDT 2004


>I still don't understand your explanation of the percentage figures for 
>leak down test because I don't understand what test flow restriction is in
>between the measured input and output pressures,


If i may step in this discussion........with the leakdown tester you connect 
the air hose from the compressor to the tester....adjust the gauge on the 
tester to 100 psi of air...make the connection to the cylinder you are 
testing....whatever the number Derek mentioned, let's say 20%.
All it is, that cylinder is leaking 20% of the air pressure going into that 
cylinder, therefore 20% leakdown on the cylinder.  So it really isn't a 
complicated tester, simply measuring what percent of the air pressure going 
into the cylinder leaks out.
Using a leakdown of course take more time than a compression test but as 
Derek pointed out, the nice thing about a leakdown it helps point you closer 
to the problem area...listening for where the air pressure is 
leaking.........air pressure from the tailpipe, exhaust valve........air at 
the intake, intake valve.......bubbles in the engine coolant, head 

John Gourley 

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