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      09-17-2012, 07:03 AM   #15
AusF20/F48
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Drives: F20 125i MS, F48 XD25i
Join Date: May 2012
Location: Brisbane

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REF: The black stains / spots on the duco around the exhaust end

This is a common issue with short curved tail pipe/s and close mounted rear back box.

When the engine shuts down after running hot, the gases still cooling in the system cause an inversion that sucks water vapour back into exhaust system, (usually worse in cold or wet weather), unfortunately as the back box is just behind the short rear pipe/s the vapour turns to liquid and accumulates in the box.

When you run the car the pipes are not long enough for the liquid/slurry to be dried so some of the liquid is caught in the vortexs around the exhaust tip lip and is then splattered onto the duco. Not a lot you can do about it.

You can get exhaust tips that have a closing flap on them to stop this, however they look crap and usually make the exhaust note sound wierd as the flap acts like a reed in a wood instrument. They work great on boats.
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