Leak Down Test

[KRYPTO]

How do you go about doing a leak down test and what importance is it to the motors health?

Should this be performed for specific reasons or issues happening?

How does this compare to a compression test?

[DaveWaters]

Doing a leak down will help you to identify where a problem is within the cylinder. To perform the test you will need an air compressor with a tank (not a tire filler), leak tester kit, and a breaker bar/ ratchet with a socket for the crank bolt. Oh and everything else you would need to remove your spark plugs.

 

Follow instructions that come with the kit.

 

The cliff notes: Move said piston to TDC. Remove oil filler cap. Apply pressure to the cylinder through the leak down tester. The first gauge tells you how much pressure you are adding the second gauge will show a lower reading (how much is holding in the cylinder) Compare the 2 readings.. for instance...100psi (gauge 1)and 95psi (gauge 2) this would be a 5% loss. There is usually a chart that comes with the tester to help with those of us who are mathematically challenged. If I recall correctly subaru states a loss of 6% or more is a problem.

 

Now to add in diagnosis of the problem....Listen for the leak. Can you hear it at the tail pipe? Do you hear it in the intake track? Or through the oil filler? If you hear it in the exhaust that would mean exhaust valve not sealed. Hear it in the intake..intake valve not sealed. If heard through oil filler ..bypassing rings. I think you probably get the idea.

 

 

Reason to do this....

 

You’ve ruled out all other reasons for rough idle, misfire etc.