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One out of the 6 of my Toyota Tacoma cylinders is mildly leaking, as indicated by a cylinder leakdown test. While other cylinders are leaking only something like 5-10%, this one leaks about 20% of the pressure that goes in while the cylinder is in TDC.

I also lose about 2 qt of oil each 1000 mi or so. I think the cylinder leaks because when I did a tuneup and head gasket change last year, I rearranged the valve tappets to meet the clearance specification and one of the exhaust valves on that cylinder was slightly off and I didn't want to wait a week to order a correctly sized replacement. Therefore, the cylinder is probably not sealing tightly.

Can it be that oil is getting into the combustion chamber because the valve is not sealing tightly?

Other than losing oil, the truck runs great. The only noticeably consequence of the oil loss is that I have to spend money on refills between changes but there is no mechanical malfunction.

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    Have you inspected the spark plugs? If there's excessive oil leakage in a cylinder I'd expect its spark plug to look different
    – Zaid
    Commented Sep 8, 2016 at 16:56
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    When the leak down test was done did you identify where the leak was exactly? Intake valve, exhaust valve, rings, head gasket....etc.
    – DucatiKiller
    Commented Sep 8, 2016 at 17:40
  • @zaid, there isn't much residue on the spark plug for that cylinder.
    – amphibient
    Commented Sep 8, 2016 at 17:52
  • @DucatiKiller, i wasn't aware there was a way to check where a cylinder is leaking, only that it is leaking
    – amphibient
    Commented Sep 8, 2016 at 17:53
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    @amphibient here is a great explanation of how you determine where the leak is. As well, zaid has a great question that's super relevant. mobiloil.com/en/article/car-maintenance/car-maintenance-archive/…
    – DucatiKiller
    Commented Sep 8, 2016 at 18:11

2 Answers 2

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2 quarts of oil every 1000 miles is a LOT of oil. Check all 6 spark plugs; one or more should look MUCH different from the rest, likely blacker and sootier. The cylinder(s) associated with these plugs is where your leak is.

Is your exhaust blue? I would expect that much oil to be pretty obvious.

Have you poked around under the car? If oil is actually leaking out of the engine, it should be pretty easy to see. If the underside is oily and/or wet, you will need to clean it off thoroughly, then run the car while underneath checking for drips.

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I am not sure of oil being burned due to leaking cylinders. Did you try a compression test on each bank to confirm whether the piston rings are worn out?

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