What is the average oil consumption of an 86 420SEL with 180,000 miles? I have noticed what seems to be a rise in oil consumption so I have started to track it. It hasn't been going on long enough to say it is a problem. Yesterday I had to add two quarts, and I check my oil every week. I park the car in the same spot every day and there is no oil under the car. The oil filter housing seems to have a very thin coat of oil on it, but does not look like a big enough leak for two quarts in a week (60 miles of driving). I have not had too close a look at the engine itself, and thanks to daylight savings time it is already too dark to look tonight. Has anyone had any experience with this model and excessive oil consumption? Before this it was arount 1 quart for 1000 miles, acceptable to me. What probable problem areas ahould I be checking.

Thanks,

JP Toronto

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Jason Priest
1986 420SEL

Jason,
I use about a quart every 800-1000 miles of driving, and I have no concerns. I just put two quarts in today, a little more consumption than usual, but still no real concerns. Occasionally I will see a small puff of blue smoke when pulling out from a light, etc... no other remarkable items other than that, and the car runs great, strong and quiet. 170K on odometer.

I have a 87 420 SEL with 230,000 miles, and I'd say you are ready for a valve job, which is common for a W126 with high mileage - had mine at 200,000. The oil loss you are experiencing is primarily around the valve stems, and new valve guides will correct that. Mine uses no oil at all now between 3,000 mile oil changes.

Thanks Hunter and Joe.

Roughly how much $$$ are involved in a valve job? What exactly is a valve job, and how is it done?

JP

Update?
 

JP, Any update. Appears I may also need a valve job. Interested in knowing what you decided to do and cost.

The problem is always valve guide oil seals. The labor by factory guide is 5.5 hours. It always fixes the problem unless you have a guide that is loose in the head. Such a condition is the only reason to do a valve job. BTW the valve job is rated at over 25 hours by the same guide.

Our procedure in cases where a large increase in consumption has occured is to pull the plugs and look for a cylinder in failure (significantly larger carbon accumulation on plug). We then do the seals on that cylinder first, looking for loose guides. If the guides are tight (as are usually the condition if the car has not been seriously oiverheated) then we proceed to do the rest of the cylinders.

It will solve the problem. It is possible that with a large amount of play in the guide to valve clearance, that the reseal will only last for 20-30k miles. Most cases it will last much longer even with guides at the wear limit.

Everybody always wants a valve job. I wonder if this is due to many shops with little experience or maybe they are just interested in the for sure fix and a weeks worth of labor. After all they will put in new seals so they are sure to fix the problem if they don't cause any new ones with major surgery.