I started getting soot on my tow car when traveling. I never had this problem until recently. The only thing I have done is remove the mud flap behind the tag axle.
I had the same problem because the exhaust was directed toward the tow hitch. I reversed the end section of the bolt on exhaust section and it now is directed to the left of the coach. Problem solved.
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2001 Newell #579
tow a 2011 Honda Odyssey
1935 Mercedes 500K replica