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Hey guys, doing a spring wash/clay and wax today and while claying the rear bumper around the exhaust and bumperettes there is a film of something that the soap couldn't get off. It took a heck of a lot of claying and it finally started to come up, and when wiped off looked brown/tan coloured. Could it be oil residue if the engine is burning oil? Never noticed it before and the only changes I've noticed in the last few months is a weird smell, more so when cold and it does seem to go through oil faster than the previous two years of ownership. I know the rms seems to leak a little but never any drops on the floor, only noticeable when up on a lift. Looks a little wet at the rms. car is an 03 C4S with 107K kms on it.
The rear bumper of the car resides in a low pressure area. As a result as the car moves down the road it collects all sorts of grime and in the right weather conditions moisture combines with this grime to make a dirty film that can be a bit more work to remove. Keep this area clean and properly waxed helps to keep the build of this film down.
Winter usage is the worst as the engine emits more stuff and with the warmer exhaust fumes contacting the cold bumper this results in more condensation.
The weird smell could be from the gasoline. Some areas switch to a winter blend of gasoline which can account for a slightly different exhaust odor.
But cold weather can also result in the converters getting started on the wrong foot so to speak or they are slower to get working and for a while (until warmed up) they can emit an odd and different odor of exhaust.
Sometimes a switch to another brand of gasoline can help.
Last but not least there is the possibility the AOS is acting up. When this acts up it routes more oil vapor to the engine, so the exhaust is a bit dirtier and oil consumption goes up.
The car has about the right number of kilometers on it. AOSs can fail between 1 kilometer and infinity...
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