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?

  • What's the vehicle in question? Each vehicle is going to have a different specification by their manufacturer. Dec 21, 2021 at 1:36
  • Toyota Tacoma 2006
    – amphibient
    Dec 21, 2021 at 1:38
  • @Pᴀᴜʟsᴛᴇʀ2 -- would you say 25% is generally alright?
    – amphibient
    Dec 21, 2021 at 4:43
  • What's the goal here? 1) I need a vehicle to get to work. How long will this one last without spending a lot of money? 2) I love my truck, and want the best for her. Is it time for an engine rebuild ($$$)? Question: How many miles on the odometer? Note: my guess for that vehicle's life is around 250,000 miles (but that's just a guess)
    – zipzit
    Dec 21, 2021 at 6:27
  • 1
    Third: the valves not seating.
    – Solar Mike
    Dec 21, 2021 at 10:14

1 Answer 1


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.

  • how do you "hear it coming out the intake"?
    – amphibient
    Dec 21, 2021 at 16:03
  • You listen... Take out the air cleaner and either put your ear down there or use a tube or stethoscope.
    – jwh20
    Dec 21, 2021 at 16:12

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