Smoke in engine compartment on cold starts, very brief - PeachParts Mercedes-Benz Forum

BodhiBenz1987 · #1 07-06-2009, 05:59 PM

... noticed something curious the last two times I started my 240D. A small amount of light gray smoke comes from the engine compartment on start-up and lasts for just a flash and then does not reappear once the car is running. This is only when the car has been sitting for a while, overnight. It also smokes very briefly from the tailpipe, and from the massive exhaust leak in the middle of the car, same color smoke, seems very normal for a 364k car that has sat overnight. The smoke from the engine compartment is new, though. I'll have to have someone start the car while I watch next time, but it looks like it's coming form the driver's side of the engine as much as the exhaust side. I did a valve adjustment recently, then it went to the mechanic to have the throttle linkage fixed ... he didn't do anything other than add a spring. Could this be related to the valve adjustment? It seems to start a little smoother since the adjustment and doesn't smoke any more or less (it doesn't smoke at all after running for a few seconds). It sounds fine and drives fine. From searches it seems smoke in engine compt. seems related to exhaust or to more major problems that would render the engine not starting or running ... doesn't quite match up for me.

Thoughts?

barry123400 · #2 07-06-2009, 06:06 PM

Oil burning off glow plugs? Have a look after the car sits the normal amount of time for your effect. That is simply because you stated the car has to sit quite awhile before the occurance. Perhaps the time required for oil to run down the side of the engine.

I do not know if the plugs get hot enough externally to burn off oil though. A warm engine has a much shorter plug duration remember. the glow Plug external heating then would be far less.

BodhiBenz1987 · #3 07-06-2009, 06:12 PM

Quote:

Originally Posted by barry123400

Oil burning off glow plugs? Have a look after the car sits the normal amount of time for your effect. That is simply because you stated the car has to sit quite awhile before the occurance. Perhaps the time required for oil to run down the side of the engine.

I do not know if the plugs get hot enough externally to burn off oil though. A warm engine has a much shorter plug duration remember. the glow Plug external heating then would be far less.

Interesting idea ... it actually does look like it's coming from that area. Also when my mechanic lubricated the throttle linkage he was extra thorough and got grease everywhere.

Any interesting theory. I'm not sure if the plugs would get hot enough externally, but watching the area while the cycle is on should give a clue I guess.

tobybul · #4 07-06-2009, 10:01 PM

either that or theres a leak at the exhaust manifold.....

Skippy · #5 07-06-2009, 11:13 PM

Mine has a leak where the exhaust manifold meets the exhaust pipe. It leaked before, was repaired, and then started again when I spilled water on it while topping up the battery. The behavior is similar. If you have someone watch that area while you do a cold start you'll know for sure.

bgkast · #6 07-07-2009, 02:16 AM

My bet is an exhaust leak. The exhaust is more er..visable on cold start up, so that is when leaks are most often found.

LUVMBDiesels · #7 07-07-2009, 07:05 AM

It could be exhaust, oil that drips onto the manifold while the car is sitting or in the worst case the starter could be smoking... have somebody crank the car over while you look under the hood.

tobybul · #8 07-07-2009, 08:35 AM

Also, check the flex part of the header pipe just after the manifold. They tend to wear out and break over time and cause this symptom.

barry123400 · #9 07-07-2009, 02:03 PM

With the car cold I imagine the castings would have shrunk back a bit more. So you might see more smoke. Plus a cold engine generates more smoke at startup. So the exhaust leak is a good possibility as mentioned.

I really do not know if glow plugs get hot enough on a full cycle with a cold engine to burn or vapourise oil off anyways. Easily hot enough to burn your fingers though.

rrgrassi · #10 07-07-2009, 02:23 PM

The exhaust pipe is too cold at initial start up to burn off any oil. I would also say exhaust leak, either at the manifold, flex pipe, or where the exhaust pipe connects to the manifold.

toomany MBZ · #11 07-07-2009, 02:27 PM

I was going to mention the exhaust as well, I don't think there is a flex pipe on a 240 tho. Doesn't mean there isn't a leak in the area, however.

BodhiBenz1987 · #12 07-07-2009, 03:59 PM

It was the glow plug ... heh. I waited about an hour for my dad to come out and start the car for me to watch, and finally the brilliant idea hit me to just run a glow cycle and watch. Sure enough, smoke started coming up off the third plug, which is the one that got covered with grease from where my mechanic lubricated the throttle linkage. Only the grease that got deep in the crevasse was burning off, and this time it was less smoke than the first time (obviously it's working its way through all the grease). I never would have thought of that. I guess it looked like that smoke was from start-up, because by the time the smoke had risen to where I could see it while sitting in the car, I had already cranked up the engine.

That said, there's definitely an exhaust leak before the first muffler, and the whole exhaust system looks just terrible. There's a patch in the middle where someone obviously tried to repair in the past, and that part actually isn't leaking. But clearly the whole thing needs to be redone at this point ... no point in adding more patches to a disastrous pipe.

Of course, I'm not really in the mood to pay $$$$$$$ for new exhaust right now ... at least I've saved by doing else myself, so I guess I can justify it.