Determining if Valve Stem Seals Are Wornm

[Mike Murrell]

Vehicle has an M103 engine - 1991 300-SEL
Some say oil consumption WITH blue/white smoke indicate worn Valve Stem Seals.

At 1st startup in the morning, after idling a min or two I see slight amts. of white smoke coming of the exhaust...white; not blue. This fades after warm up...no coolant loss at all.
I live in a high humidity area.

I know about the M103 guides/stems and oil consumption. What about this blue/white smoke issue? If the Valve Stem Seals were worn, would I see blue/white smoke ALL of the time or just at specific instances? Thanks for your time.

Mike Murrell

Mike,

I am not an expert on your particular engine, but I am familiar with valve stems seals, having had the problem on a water cooled VW years ago.

Worn valve stem seals will cause oil consumption. The start up will result in a white/blue smoke. It has a distinctive pungent smell and lingers. Surely you have been stuck behind a car that is a "Mesquite Fogger" and have rolled up the windows to minimize the acrid smell? With worn valve stem seals, after warm up, the emission of blue smoke stops, although the worn seals will continue to leak oil into the combustion chamber and cause mild oil consumption. The amount is small enough that it is not visible in the exhaust after warm up. You may see some slight wet blackness on your spark plugs. A light tan color is the desired condition.

I believe you are seeing one of the by products of combustion, H2O. Any internal combustion engine produces H20. A cold exhaust system causes this water vapor to condense in the muffler. As it continues to warm up, the hot gases cause the condensed water to turn back to steam. Eventually the whole system gets hot enough, that the water is purged and the vapor content low enough that it is no longer visible. It is not unsusal for a cold car to actually drip water out the tail pipe.

Sounds like your car is fine. If you have any doubts, let some one else start the car and you can stay in the back and smell the exhaust! Just don't breathe it too long, it's addictive!

I will come out and smell the exhaust for a small fee if you are still unsure !

Best Regards,

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Deezel
87 300TDT
150,000 miles

Mike,

Deezel is right on, but you never said how much oil the engine is using, if any.



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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in
Mercedes automobiles

[Mike Murrell]

Deezel - Thanks so much for your time and the overview

Larry - I think I have a leak more than internal consumption. I used synthetic awhile back and noticed consumption went up noticably afterwards. I switched back to "dino" oil. When I pull the large plastc shroud from the bottom, I see eveidence of oil leaking down from around the distributor. Does anyone know if this would be oil leaking past a distributor seal or is it coming from the head gasket. I realize I need to look, just searching for the most likely causes of M103 leaks from around this area.

There is one thing that REALLY seems strange to me and the condition I'm about to describe also happens with a '95 Rodeo V-6 3.2 liter engine.

After an oil filter change, I can go approx 600-800 mi. without any oil loss. After driving approx 600-800 mi. I begin to use about 8 oz every 250-350 mi approx. You drive another 250-350 mi, then an 8 more oz. I change my oil and filter every 1,500 mi. After the oil change, everything is fine for 600-800 mi, then I go thru the whole thing again....lose 8 oz or so every 250-350 mi ??
Why the engine seems to stop leaking temporarily after an oil/filter change is beyond me?

Thanks to all of you veterans on this site that help diyers like myself.

Mike Murrell
Boerne, Texas

Mike,

I experience the same accelerated oil usage with my old 240D. The only explanation I can come up with, is that the oil gets a little sheared and is quicker to make it past all the areas where you don't want it to pass. Any comments from anyone else about this would also satisfy my curiosity.

On the M103 engine, it is common to see a leak at the bottom of upper timing cover at the front of the engine. There is a seal at the bottom of this half round looking cover that commonly has a slight leak. I've been keeping an eye on mine for about 80,000 miles. It wets the front passenger side of the engine just a little, but doesn't drop anything on the shop floor. When it starts leaking bad enough to leak on the floor, I'll pay it some attention. Unless it's leaking enough to stain the floor, I'd wash the engine and then keep a close eye on it. If it is a bad leak, wash the engine to determine for sure where the leak is coming from, and then fix it as soon as you can.

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
Over 800,000 miles in
Mercedes automobiles