Another leakdown testing question Options

[rtalich]

Connecting air to the tool and setting the pressure so that the first gauge reads 100psi BEFORE connecting to the cylinder. When I do connect to the cylinder, the pressure drops a bit. Do I re-adjust back up to 100psi before taking my % reading?

Thanks,
Rob

[DNHunt]

A leakdown test tells you how much air is leaking out of a cylinder. It uses a regulator to set a pressure of ~100psi annd a second gauge to read the pressure after the whole thing is connected to a hose screwed into the spark plug hole. The second gauge is usually calibrated in % so something close to 100 percent would indicate a catastrophic failure. A new engine will have a really low leakdown number. This is usually done a warmed up engine at TDC.

It can be useful to help find where a cylinder is loosing pressure also. If a person hears air hissing when you put your ear at the oil filler it suggests blowby and poorly sealing rings. Hissing from the intake suggests a problem with the intake valve, noise from the exhaust, the exhaust valve. Bad head leaks can sometimes be heard. It helps to pinpoint problems.

Dave