Piston Slap: Hunting down the right fix for Montero oil consumption

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Piston Slap MItsubishi Montero side profile
Danny (OP)

Danny writes:

Hi Sajeev! My ’91 Mitsubishi Montero is showing signs of valve stem seal failure: the engine shows good compression but burns oil excessively (especially when cold) and one of my spark plugs gets consistently fouled out with oil deposits. Originally I was looking at just replacing the heads completely with remanufactured examples, but some members of the Montero Facebook page seem confident that I should just replace the seals in my existing heads and enjoy smoke-free driving.

Remanufactured heads are fairly cheap, roughly $300 each, but valve stem seals are less than $1 each. I’ve done a timing belt and water pump before on my IS300, so this doesn’t seem too far beyond my capabilities, unless I’m missing something. Is there any great advantage to rebuilt cylinder heads, or am I taking a gamble on their condition? I drove the truck 2000 miles home from Montana last year with this issue, so another option is to just keep driving it as is and adding oil, but I’d like to be running consistently on all 6 cylinders.

Sajeev answers:

Rebuilt cylinder heads are great in theory, but it depends on the quality of the rebuilder. Since you still have good compression, odds are you are only seeing blue-white smoke upon cold starting, or upon initial acceleration after long periods of idling (when engine vacuum is the highest). If so, it’s just oil passing by failed valve stem seals. And $1 each sounds like a mighty affordable repair, for someone with your mechanical aptitude.

I’d worry about replacing the cylinder heads when it’s time to replace the rest of the motor: Just get a remanufactured long block when the time comes. We discussed the procedure for changing valve stem seals in the past, and I’d get a compressed air tank and the appropriate threaded insert for the spark plug holes to make this job easier. It sounds like you might not be in a hurry to fix it, so perhaps this is be a good wintertime project!

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