1985 Mercedes Benz 380sl Leaking from Exhaust Pipe

  • 1985 MERCEDES BENZ 380SL
  • 94,600 MILES
Oil leaks from where the exhaust pipe connects to front of the catalytic converter. I have observed this while the car is idling. I have not driven it since this started. There is also smoke but I cannot determine the color, but it starts out black, then evolves to gray/white. The valve seals look good, but they could be marginal. As I stated in the last question on this problem, eventually smokes comes out of the engine area. The longer it runs, the thicker it smoke. Why? (I could not figure out how to do a followup question).
Do you
have the same problem?
Sunday, September 29th, 2013 AT 1:49 PM

1 Reply

Hi charlestuck, caradiodoc here. You should get an automated e-mail with a link directing you back here whenever a reply is posted. At the bottom is a button to click to post another reply, then click on "submit" like you just did. That way we can keep the conversation going.

First of all, there is usually a drain hole in the bottom of the muffler to allow condensed water vapor to escape. It will drip on the ground near the middle of the car, and it will often have carbon in it making it look black. Dripping is normal; oil is not. Nothing should leak from the connections between the exhaust pipes.

Is it possible you're seeing water dripping from the air conditioning system? There is a drain pan at the bottom of the dash to collect the humidity that condenses on the cold evaporator. That water drains out from a tube under the hood, on the firewall. There's a 4" long rubber hose with a 90 degree bend hanging down to prevent entry of bugs and debris, and to direct where that water drips. If that hose fell off, that water might drip onto hot exhaust parts, then it will follow it down the pipe until it drips onto the ground. That would make steam too that got worse when the pipes became hot, and the longer the air conditioning is running. The clues here are the oil level and coolant level would not be going down. There also might be evidence of that dripping in the form of a discoloration on the top of the exhaust pipe where the water hits it that is nowhere near a joint.

If this really is oil, the level would be going down in the engine. One possible cause is a leaking cylinder head gasket, but that would not be common. Typically when they leak, they leak coolant. Coolant in the combustion chamber will cause white smoke from the exhaust, and the level will go down in the radiator or reservoir. The symptoms can change too as the engine warms up. At first any coolant that snuck into the combustion chamber after the engine was last turned off would get pushed into the exhaust system where it could drip from a pipe connection, but eventually it would be hot enough to turn to steam and make white smoke from the tail pipe.

Common causes for oil smoke or oil in the exhaust would be the level is overfull, the PCV valve is blocked so the fumes can't be drawn out and burned, there's excessive gas in the oil from a previous running problem, the oil is the wrong viscosity, or the valve guide seals are worn. With worn valve guide seals, oil will run down the valve stems into the combustion chamber where it is burned. That causes blue smoke from the exhaust which is almost always much worse right after a cold engine is started. That oil ran down overnight and collected in the combustion chamber. When the engine is started, that oil gets burned and pushed into the exhaust system. After few minutes it is burned out, and the oil that continues to run down the valve stems does it so slowly that you'll barely see any smoke. Evidence of fuel in the oil is the smoking will be less noticeable the more the engine is run, particularly at highway speeds. That give the fuel time to vaporize and be drawn out and burned.

Give that you're seeing the smoke under the hood, if it's not water from the air conditioning system, it is most likely due to an oil leak outside the engine, and that oil is dripping onto hot exhaust parts. Leaking valve cover gaskets are the most common cause. Here again, the clue would be the oil level is going down as you drive, and to be leaking badly enough to cause smoke, I suspect you would see the level drop a noticeable amount after driving just a few dozen miles.

Rather than fret over what could be a very minor problem, or allow a minor problem to cause a big one, have a mechanic take a look at it, even if it is just to determine the cause and the possible ramifications of driving the car that way. Once we know the cause, it is easier to determine how to proceed.
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Thursday, October 3rd, 2013 AT 1:14 PM

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