I did a cylinder leakdown test on my 6 cylinders and they range at 75-80% retention, meaning 20-25% leaking. What is an acceptable rate of cylinder leaking?
If the leak in a certain cylinder is higher than that threshold standard, is it more likely the problem be in piston rings or the head gasket? Or something third?
A leakdown test is not go/no-go. It's somewhat subjective and the about the most important factor is not the leak percentage but WHERE that leak is going.
If you have 20-25% leakage and you can hear it coming out the intake, then you likely have a stuck or bent intake valve and you need to repair the head. Same with the exhaust.
If you have 20-25% leakage and it's coming from the crankcase, then you have a piston ring problem or something like a cracked or burned piston.
If the air is bubbling into your cooling system you have a blown head gasket or a cracked block/head.
Another important factor is the reading on the other cylinders. 20-25% is at what most consider to be the high end of "normal" but what normal is depends on what the manufacturer says it should be. A spec of 20% leakdown is not uncommon to see in a service manual for an engine. So you may or may not have a problem depending on the specific engine in question.
My guess is that your engine is relatively high mileage and has some wear but unless there is a big difference between cylinders there is still plenty of life left in it with respect to the things measured by the leakdown tester.
