OM642 Carbon dust on underside of turbo heat shield
 

Hi all,
Doing a routine check of my OM642 turbo actuator rod, I noticed a good amount of powdery carbon build up on the underside of the heat shield. I could not see any obvious traces of carbon on the turbo body exhaust side with the exception of a slight trace from where the actuator arm enters the turbo body.

I did notice a slight amount of carbon on the main exhaust pipe to turbo connection down low in that corrugated metal union between the turbo exhaust pipe and the rest of the exhaust, but most of that is not under the heat shield and the surrounding areas seem fairly clean. Felt around for leaks but did not detect any by hand.

Any ideas as to why the underside of the heat shield is covered in carbon?

For now, cleaned up the area and cover and will monitor. The actuator arm moved freely in the turbo body, wondering if that little pass thru is the source of the residue. any observations, or experience others have had is welcomed.

TIA

I had the flex pipe develop a crack, which resulted in carbon coating the adjacent areas. In my case it was more on the heat shield on the firewall, but I suppose it depends on where the crack is located. Replacing the flex pipe was easy and straightforward. I do recall it required new one use only bolts on the turbo side. It’s been several years and that w211 is long gone, so afraid that is all that I recall.

My W211 OM642 had a good bit of carbon buildup on the firewall heat shield as well. I cleaned it off and it doesn't appear to be returning too quickly, but good to know about the flex pipe. I also wondered if a leaking turbo inlet seal could be contributing. Mine was very old and was not sealing properly, but it has since been replaced.

This trick best done at night.

Get a strong flashlight (preferably one of those LED light bar style with a back shroud) and hold it horizontally just below eye level, bend down at the fender, and start hunting for the smoke with the engine running. This is before any of the pollution controls so you will be able to spot the rising smoke and probably can smell it too.

Found my 90 degree EGR pipe had a loose joint, needed to be properly torqued. Someone was there before I got the car.

Thanks for the great suggestions folks. Will try the light trick as well Jay Bob, and report back on my finding.