I recently performed a cylinder leakdown test searching for a cause for oil loss. On 5/6 cylinders, I pumped it up to 90 psi on the left gauge and the right gauge was between 75-80. Only 1/6 wouldn't go past 65. I put my hand on the intake for that cylinder on the plenum and didn't notice and leaks, then put my hand on the exhaust pipe and there was maybe a very low flow. The air may have been going past the cylinder rings and into the crankcase but I'm not sure how to check that.

How bad is a 30% leak, especially if it's on the exhaust side ?

  • 4
    You check airflow into the crankcase by pulling the oil filler cap.
    – Ben
    May 7, 2016 at 17:07
  • and you're sure the exhaust valves were closed?
    – Ben
    May 7, 2016 at 17:15
  • If they weren't closed, I'd be getting 0. I did the test on that one multiple times
    – amphibient
    May 7, 2016 at 17:21
  • 30% indicates a problem. how is compression and engine vacuum?
    – Ben
    May 7, 2016 at 17:25
  • @Moab Put your comment as the answer. May 7, 2016 at 22:34

1 Answer 1


"put my hand on the exhaust pipe and there was maybe a very low flow."

You have found your problem, there should be 0 flow.

  • Additionally this sounds like a possible bent, or burn valve or valve seat. Recommend taking a look inside of the cylinder with a borescope if possible. I'd hazard that there's carbon build up on the valve preventing effective sealing. Anything short of taking the head off would be guessing. May 8, 2016 at 10:36

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