Explain to me Leakdown tests
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 2,152
Likes: 243
From: Northern VA
Explain to me Leakdown tests
Still trying to track down my massive oil consumption. Compression test showed between 175 and 180 for all cylinders. A leakdown test showed #1 =16% #5=16% #2=10% #4=12% #6=8% #8=12%
What does the leakdown test show and what do the percentages mean? Mechanic could not get the tester on all cylinders but what do the above measurements indicate if anything? I have pulled plugs and #3 and #5 were especially black. Not necessarily oiling but highly carboned. A paper header gasket was soaked with oil at this location as well. Any ideas?
Thanks
What does the leakdown test show and what do the percentages mean? Mechanic could not get the tester on all cylinders but what do the above measurements indicate if anything? I have pulled plugs and #3 and #5 were especially black. Not necessarily oiling but highly carboned. A paper header gasket was soaked with oil at this location as well. Any ideas?
Thanks
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
In your case the compression and leakdown tests are not conclusive about the source of oil consumption. Low compression and/or rapid leakdown can mean worn rings or excessive piston to cylinder clearance contributing to blowby and oil burning from the poor performance of the oil rings. However, black plugs and oil soaked header gasket could come from excessive valve stem to valve guide clearance letting oil enter the cylinders. If after waiting at a light you experience grey smoke upon acceleration and/or smoke at startup, then head overhaul is indicated which should stop oil getting through the valve stems into one or more cylinders.
Thread Starter
Melting Slicks
Joined: Jun 2002
Posts: 2,152
Likes: 243
From: Northern VA
I will look at the TB and try to peer into the intake this weekend. Boy, I would hate spending the time to pull the heads apart only to find out it's the rings. I guess the leakdown test is ok?? I sure hope it's only the valve stem seals.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Those higher leak down numbers are cause for concern. The black plugs likely mean an overly rich mixture, that may have taken a toll on the rings. The header gasket sounds more like a leaking valve cover gasket, than anything else. When the cylinders are under pressure, you can listen for escaping air, to help pinpoint the problem. Crack the throttle and listen at the TB for an intake valve problem. The mufflers for and exhaust valve, and pull the oil filler cap and listen for air passing the rings into the crankcase. If bubbles rise in the radiator, it's likely a head gasket.
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by jerkyboy
what would I be listening for out of the exhaust and TB? What type of sound? Any chance that this could be valve seals?
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