Intermittent exhaust leak?
 

I have a 83 300D that has been in the family for decades and I am in the process of bringing her back to her glory. Good thing is my Father was meticulous about service and I have all records going back to when he bought it CPO in Princeton only a few years old. Bad thing is he had a mild stroke about 5 or so years ago and the car basically sat except for a run here and there. It did have some recent work in 2012. I drove it down from NJ to FL in October with no issues other than dash light rectifier went out(anyone have a source that is not $100?). I have done all the maintenence like brakes, fluids, etc and mechanic gave her a green light. Move forward with no issues until about 3 weeks ago and.....

I have put over 2k miles since NJ and recently I have an exhaust(?) leak. At low speeds it sounds like a "single" cyl leak ONLY when the turbo kicks in. As soon as I let off the gas it goes away. It does this in all gears but not all the time depending on temp(engine & outside).Once I start getting into the 50mph range it starts getting louder again. Now if naturally aspirated I would know what my problem is. Turbo could be a manifold gasket, flex pipe, turbo hose, or ?? I thought about just going in there and torquing all the nuts and see what happens but I figured I would start with the diehard W123 guys. Again if I am easy on the gas it is non existent, I would assume manifold would be leaking 24/7.

Lastly....when I used to drive this years back I could stop traffic with soot if I laid it out. Now I add some diesel clean mixed with about 5 ounces of 2 stroke for lubricity with low sulpher fuels and this baby is almost as clean as my 2014 Jeep diesel. Ok...not really but she blows VERY little soot. Because of low sulpher? more aggressive(not beating on it) driving? I know I have a small vac leak due to center AC pod but she still feels pretty strong power wise, but again I have not driven another to compare. I also heard a small exhaust leak can kill the power on these cars. Working on vac leak to restore smooth 1st-2nd shifting.

PS....244k miles

Inspect the exhaust system and look for spots of soot. If you have a hole somewhere, the exhaust will make it look like a sooty line away from the hole. Check the flex pipe and gaskets. Check the joints where exhaust pipe meets exhaust pipe. I had the strangest noise for a few weeks that drove me mad and it was due to a loose joint where the rear muffler section bolted to the straight run below the driveshaft.

I should have some time this long weekend. Wish I had access to a lift. It is definately under the hood.

May be the manifold to head gaskets .This can be a big job .The fixing studs and nuts go rusty over time .And brake off as you try to remove them.So the next job then is to remove the broken stud thats stuck inside the cylinder head...I made a jig ,but only for the petrol engine w123 dont know if the layout is the same on the diesel .

"...I have an exhaust(?) leak. At low speeds it sounds like a "single" cyl leak ONLY when the turbo kicks in. As soon as I let off the gas it goes away... into the 50mph range it starts getting louder again."

-your description would seem to indicate an issue with the waste gate. The exhaust pressure ahead of the turbo increases with acceleration & load, sometimes to a point where the waste gate has to open to relieve excess pressure. Check the adjustment, and waste gate components for proper operation before proceeding.

"...I could stop traffic with soot...I have a small vac leak..."
-assuming that you haven't done anything to the fuel injection system & pump, a decrease in soot is most likely a byproduct of cleaner fuel, not a vacuum leak. Unlike a gasoline engine, the vacuum with a 300D is generated by an external pump, not manifold vacuum.

-a word of advice: before putting a wrench to any part of the exhaust system or any bolt/stud attached to the block, head , exhaust, turbo, etc soak the fastener in penatrant (Kroil, atf, PB blaster, WD-40, Liquid Wrench, etc - your choice)

Biggiefl,

In your first post you talked about a rectifyer for the dash lites. I suspect that you are referring to the rheostat for controlling dash lite brightness. Many on the forum here have simply jumpered across the rheostat to get lights back. Particularly since the brightest point in the rotation of the knob is none too bright anyway.

Maybe his Rheostat just needs cleaning.
PeachPartsWiki: Dash Light Rheostat Rebuild



Charlie

I dreamed once my exhaust manifold fell off when driving.That morning after waking up,I found my bolts needed up to 4 turns to tighten.

Yes the Rheostat is bad. Weird is plastic reset knob, not brass. Gotta see hat somebody tried to modify.

Noise went away again. I will try and tighten manifold and look for a leak etc. I know enough about engines not to snap stuff off. Highly doubt its the waste gate blowing off boost as there would be soot if I was boosting that hard.

Thanks for the help so far.