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Hagerty Employee

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

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 ... Read the full article on



I ordered the seals, as well as a timing belt and water pump since I'll be pulling the rocker arms off and might as well change those (no idea when they were last done). Thanks!

Community Manager

Agreed, it's time for a good engine service all around! 


I think the larger question here is if the engine is an overhead cam or just overhead valve configuration.  If it's an OHC, depending on how it's designed, getting to the valve springs and retainers could be pretty in depth, whereas an OHV design is typically very straightforward.


Community Manager

Good point,VERY good point in fact!  While this is a SOHC motor, I'd still wager it's worth the effort to deal with all this mess in lieu of buying a reman head of unknown quality and hoping you get something better than what you got.  

Intermediate Driver

Here's the risk you face with supporting the valves with compressed air: there's a good chance the piston can be pushed down, because there really isn't anything stopping the crankshaft from spinning, and when that happens, you'll see the valve drop into the cylinder, and the only way to recover from that is to remove the cylinder head. This happened to me on a Sunday afternoon, and I ended up re-using the same head gasket with no problems after 10 years and probably 80,000 miles. I remember having more success not using compressed air, and I think I had a breaker bar with a socket that was used to prevent the crankshaft from rotating. I also think I might have only replaced the valve stem seals on the one cylinder head I ended up removing, because the originals were not as worn as I imagined, and were still pliable and tight. I can't help but wonder if the problem might be a bad positive crankcase valve allowing oil vapor and blow-by to get sucked into the intake manifold, and by virtue of the design of the intake system, it happens to be cylinder 1 that gets loaded with heavy oil particles. So I would take a close look at the PVC valve to see if oil is entering the intake before I do major work on the heads, and I would also try an oil stabilizer, and see if that helps.