My W126 motor going bye bye?
 

So I took the 126 to another trip from LA to SF and back. Last time I did this, I noticed a couple of times when the car billowed blue oil-smoke for short periods.

On the way to SF, not a single problem. It ran like a top and I arrived to my destination smoothly. Drove it on I-5 for about 300 miles at an average speed of 80mph. Fuel consumption was around 19mpg.

On the way back to L.A., it had about 5 to 6 20-30second episodes where thick blue smoke billowed out. These were short isolated moments where the car just spewed blue smoke uncontrollably. The engine sounded fine when it happened and no systems seemed to run any worse for it. These episodes happened during steady cruising at around 75-80mph. Not during any acceleration or up any hills or during anything particulary strenuous. The smoking would stop as quickly as it started and the car would run fine until the next randomly designated time to smoke.

I did notice the smoking got thicker when I let off the gas.

The car does not emit any smoke at startup, during daily cruising around the city, and does not drive strangely. There are no dripping fluids on the ground. The smoking does not happen all the time. These appear to be little isolated episodes that I can't seem to attach to anything in particular... it just happens for a little while and it sucks while it happens, but then it stops.

Anyone have an idea as to what's wrong? Is this the engine being worn?

I maintain the car as well as I know how to - monitoring oil level, oil/filter changes every 3K miles, everything else is up to date. I always use Castrol GTX 20W50.

Is it time to switch to Synthetic? Is this just a stopgap measure? Is a motor rebuild/replacement the only option left? Does this sound like a top end issue (worn valve stems/guides?) or a bottom end issue (worn piston rings). I just don't understand why it doesn't ALWAYS or at least, often, smoke.

The car has 196,000 original miles. I've owned it since it had 150,000.

Thanks.

You don't need synthetic. What is the rate of oil consumption? Have the valve stem seals ever been replaced? Has it ever had a compression or leakdown test?

Also suggest you do a thorough inspection of the PCV system (number one suspect). Is there oil in the air cleaner? Engines rarely just go away suddenly. They degrade slowly over time. You apparently have a problem, but it is probably not major.

Duke

If it was bad rinjgs, the smoke would be constant, especially under acceleration.

What car is it? Is it a 300, 420, or 560? The 300's are pretty bad for oil consumption, so I've heard.
Thanks
David

(EDIT), sorry. I just looked t your profile which I should have done earlier, my apologies. The 380 is notorious for chain failure, and I think yours is an '83 if I remember correctly. That was 1 year before the engines were converted. You probably know all this though.

I would bet it's valve seals. 200k miles seems to be the time V8 Mercedes' needs them done. I would think that with guides it would do it all the time. To do this job by yourself you going to need the right kind of spring compressor. NOT the ones at autozone, they have to have been designed for OHC engines.

Didn't the M116 3.8L sedans all have the double row chain? Can't recall where I read that, but I might (high probability) be wrong.

Doesn't sound like the bottom end. A leak-down and compression test should get you to the bottom of it (punny) but I'd check the EGR and vacuum lines first, just in case. Does the car have any oil leaks?

more data
 

This is a 380SE Euro version (graymarket) W126 chassis. It currently has 196,000 original miles on it.

I had the timing chain + guides + tensionners + water pump replaced at 160K miles. So I've put on about 36K on the new chain and tensionners etc.

I have never checked the EGR valve nor any of the vacuum system.

I tend to think the bottom end is not to blame because the smoke is so rare and intermittent. It's just that on the rare occasions that it does smoke, it smokes a lot for about 20 seconds at a time.

The car otherwise does not have any known leaks. It does not drip any oil on the ground. I do put in about 1 qt of oil every 1,500 miles or so - more when city driving, less when mostly hwy miles.

Check the cam oiler tubes and retainers.

(126nut, aka tex)

I had a chevy V8 that did the same thing for a few weeks then healed itself,my only explanation was that the gap in the rings were sticking in lined up position.......

William Rogers........