1985 Mercedes 380sl smokes from exhaust under hood on curb side and from tailpipe

Tiny
CHARLESTUCK
  • MEMBER
  • 1985 MERCEDES BENZ 380SL
  • 94,600 MILES
The car had not been run for 12 years. My car starts super fast. As it warms up, smoke comes from exhaust under the hood on passenger side and out the tailpipe. As the car warms up the smoke get thicker and floats through the air. The smoke coming from under the hood tapers off. When I take off, the smoke (blue/white) creates this dense fog of smoke. After a few blocks and acceleration, it clears up. The car runs smooths throughout all of this. I replaced the fuel pump, filter, tank strainer, drained and refilled the tank, removed and flushed the fuel distributor, replaced spark plugs, distributor cap and rotor button, and ran Chevron through vacuum line and put a bottle of Chevron in the gas tank. (I have driven probably 20 miles since running the Chevron through the vacuum). I also removed the injectors from the passenger side and soaked them and I blew compressed air through them. The driver side spark plugs were wet when I removed them and the plugs from the passenger side were dry. The passenger side plugs tips were black, but dry.
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Friday, September 6th, 2013 AT 11:16 AM

4 Replies

Tiny
CARADIODOC
  • EXPERT
Blue smoke is a sign of burning oil. It is likely, due simply to age, the valve guide seals are hardened and cracked. In addition, from sitting for that long they are likely dry-rotted. That will allow oil to run down the guides and into the cylinders where it is burned. Since it's a lot thicker than gasoline it will take a few minutes to completely burn off. Once the engine is warmed up the oil runs down the guides too slowly to cause noticeable smoke. At start-up that oil gets blown into the exhaust system where it takes longer to get hot enough to burn the oil off.

This smoke can also be caused by the engine oil being diluted with gas. I'm guessing you changed the oil already but there's always a couple of quarts that don't drain out. I've had a few cars that smoke at start-up for a few minutes. The problem always seemed to clear up after about two weeks.

On most engines the valve guide seals can be replaced without removing the cylinder heads and valves. There's a special compressed air hose that is attached to the spark plug hole, and that air keeps the valves closed so the springs can be removed. You can also stuff a piece of rope into the cylinder, then bring that piston close to top dead center. The rope will hold the valves closed, and can be pulled out when you're done.
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Friday, September 6th, 2013 AT 11:36 AM
Tiny
CHARLESTUCK
  • MEMBER
Is it possible that piston rings are stuck? Why are the spark plugs from the driver side wet and the ones from the curb side dry? Well, 3 from the driver side, I couldn't get one of them out. How do you suggest that I get the stuck plug out? It turns a couple of turns.

Thanks.
Charles
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Friday, September 6th, 2013 AT 11:54 AM
Tiny
CARADIODOC
  • EXPERT
If a piston ring is stuck you'll have excessive blowby. That will get sucked out and burned without causing smoke. If an oil control ring is stuck or broken you'll have blue smoke after the engine is warmed up. The thinner oil will get past the rings easier.

I never paid attention to the wetness on spark plugs. If it dries off quickly, that is gas that likely sprayed into the cylinder after the spark stopped when you stopped the engine. If it stays wet, it is engine oil that ran down from a valve guide. Whether or not it drips onto a spark plug depends on whether that valve is open or closed.

If a spark plug comes out a couple of turns before it gets tight, that is due to excessive carbon buildup on the threads. There are decarbonizer products that may solve that. Some products are sprayed into the fresh air intake. Do that fast enough to stall the engine, then let it sit for a few hours. Run the engine again to break that carbon off. When you have a mass air flow sensor that chemical should be introduced after it. That usually involves finding a vacuum port. The best place is in the fresh air tube right after that sensor but be aware that any air leak in that tube can affect how the engine runs. That air that's sneaking in won't be measured by the sensor so the computer won't command a corresponding amount of fuel to go with it.
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Friday, September 6th, 2013 AT 12:35 PM
Tiny
MADMIKE1735
  • EXPERT
Have you performed a compression test? If not, try it out. You need to pull the spark plugs. Obviously right? Once the plugs are out, check them. Look for any excess carbon build up. Your sparkplugs can tell you a story of whats going on inside the engine. A dry, then wet compression test can verify. If cylinders test ok, try doing a block test. This will verify any combustion leaks.
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Tuesday, October 1st, 2013 AT 6:47 PM

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