Well after 3 long weeks of rain, I was finally able to give the car a wash...what I thought was caked on grime on the rear were actually little black dots of exhaust soot.

So... I'm gonna think 2 things may have caused this...

1. Regular 87 octane was used once or twice as a test of how the RDX would run on reg. (I wont be doing this again)
2. Using lower tier premium gas from a shop called USA Gasoline instead of Shell .

I noted that 'oil life' minder is down to 30% so an oil change is coming also.

Previously, I only used Shell 91 and never had this issue.

anyone had similar experiences?

 

That is NOT caused by 87 octane gas. Unless you've been burning diesel, the "soot" is either what you first suspected (road grime) or it is oil. Have you checked your oil level recently?

 

Have you driven on any newly paved roads lately?

 

^^ no driving on newly paved roads... just idling ALOT lately..sitting in stop and go traffic. it's never happened before so the only 2 different 'things' ive done are noted in original posting.

Will check oil when I get home....and to check if its just grime that was spit up on the rear, i'll check the tail pipes for excessive buildup perhaps.

 

Any wet, dirty, dusty roads? Unpaved roads? Has it been misty or foggy near you recently? Moisture attracts dirt.......

 

West coast....we have had torrential rains....heavy heavy rain.

Checked exhaust pipes....no real major buildup other than your usual stuff....I'm gonna go with the black stuff as road grime for now....I've forgotten how dirty cars can get especially flat back SUVs when not washed for weeks and driving in the nonstop rain.

 

I would highly doubt you have exhaust soot on your car, unless there is something seriously wrong. Driving in lots of rain will cause all kinds of interesting dirt to be deposited on the car.

 

Driving in the Northeast, I get a similar effect when driving in the winter with salt/sand on the roads. I didn't have the RDX much last winter, but the times I did drive it in those conditions, the amount of stuff kicked on the rear was pretty amazing. Plus that rear "wing" over the back window seems to really create a vacuum that sucks even more stuff up to the rear window (at least as compared to my '13 MDX which attracted much less). I'm betting it was just all the road junk kicked up from the rain and normal driving.

andy

 

Older diesels and manual transmission BMWs are the only ones that get "soot" unless there is something terribly wrong and you'd see that on your dipstick.


It is just plain old road grime.