I just spent $1200 to have two exhaust leaks fixed on my '86 300SDL. It cost this much because the repair entailed removing the entire exhaust manifold and turbocharger, as well as the use of lasers. (Yes - lasers!) That's the bad news, though. The good news is this repair has taken care of other issues I was having that I thought were not really related, so I thought I might share it.
The original symptom was smoke coming out of a crack in the medium sized accordion fitting between the turbocharger and the rest of the exhaust. It turns out that fixing that required removing most of the exhaust manifold! When it was out, my mechanic identified that there were two bolts that had the heads sheared connecting the manifold to the cylindar head, creating another sizable leak. This is where the lasers came in: my mechanic didn't want to risk removing the bolt himself because of aluminum cylinder head and their inaccessibility, so he had the car delivered to a place where they use lasers to disintegrate the bolts. He surmised the Trap Oxidizer caused the bolts to break because of the high heat it produced. According to MBNA, however, that is not a warrantee issue.
With the turbocharger out, my mechanic noticed some hoses were disconnected and replaced those. Of course, he replaced all the bolts, seals, and gaskets since everything was out. After getting the car back, I noticed a bunch of things were fixed, some of which I wouldn't have suspected, but now make sense.
- No more exhaust smell in the cabin (very important with our baby arriving soon!)
- No surging when the car hits 4000+ RPM. I suspect this had to do with the disconnected hoses in the turbo wastegate triggering the overboost protection as much as inconsistent exhaust pressure.
- Lack of power. I can vouch the OM603 engine is gutless w/o the turbo. I didn't realize how much until the turbo started to work again. I'm hoping my fuel economy increases from the abysmal 21-22 mpg I've been getting.
- The real surprise. My engine runs much cooler. Before, when I idled with the a/c on, the needle would get to 105, even w/ a new T-stat and fresh coolant! I thought I had the dreaded crack in the cylinder head. Now it runs at 85-90 at idle. I'm guessing the hot exhaust gasses that were leaking prevented the engine compartment from cooling properly, causing the temperatures to increase.
If you have an OM 603 engine, I suggest having it checked for exhaust leaks, as well as checking to make sure all your turbo hoses are connected. I spent $1200 to fix mine, but with all the problems it resolved, it was a bargain.