black deposit on tow car from engine - problem?

[DaveG39]

I just bought a used motorhome with a 2007 Cat c7 350hp engine. After driving all day I noticed some black, sooty deposits on the hood of the car I was towing that looked like it may have come from the motorhome engine exhaust. Is this normal or does the engine need some sort of adjustment? The engine runs fine and was a smooth ride. No indications of malfunction on the Freightliner computer print outs. I have never had a diesel engine before and do not know what to expect.

[94-Newmar]

Dave,

I'm not sure if your 2007 model is equipped with any emissions filtering such as a DPF (Diesel Particulate Filter) or not - but if it does and you have soot then its best you have them check it out again. The DPF's started showing up on many diesels during the time your unit was built in 2007 for the upcoming mandated DPF requirements for 2010 models.

If it was not equipped with one and its a dry powdery deposit that wipes right off then it is most likely diesel soot. Check around the outside perimeter of your exhaust pipe - If you see a black ring on the outside of the tube then what you're seeing on your car is most likely just soot. If the deposits are really oily and leave streaks when you wipe them off I would check your crankcase breather tubing; make sure its exiting properly at the bottom of the chassis and that there isnt any excess oil dripping from it which could blow back onto your toad. There are crankcase breather filters that are used to control that but I certainly wouldn't think a 2007 model would have that much crankcase blowby.

[Pat Z]

There are at least 2 possibilities one is road grime and rubber kicked up by the RV, the other is oil mist coming out of the breather ttube on the coach. There are a lot of posts here on correcting that one, from extending the breatger with PVC to rigging a plastic bottle with steel wool and vent holes on the pipe to catch the oil.

[hondo122]

Dave, check out CAT RV Club they have had many discussions about this.

[DaveG39]

Thanks all. I joined the CatRV forum and am going through all the comments.

[Pusherman]

Most likely it is 'blow-by' oil coming from your slobber tube from the engine. This happens more frequently especially if the engine is overfilled with oil. Cat C7's like 19 quarts. More than that it will blow out the slobber tube and end up on your toad.