Topic

Right, lets cover the basics
Water is clean and is not being lost
temperatures are fine
oil is spotless
caps, dipsticks etc are all fine
fumes show no evidence of blue or white smoke when under load or at idle

now the issue
over the course of three weeks driving I have notice that the rear of the car is getting a lot dirtier than the rest. (300 miles ish)
Close inspection finds a residue on the rear end - presumably from exhaust fumes. Feels a little oily but not overly so. More of a dark brown grease colour than oily black. not a thick residue - just there enough to cause allt he road crap to stick.

Any ideas?

Have you changed your car washing detergent or polish recently? Could it be as simple as maybe needing to use a good grease cutting cleaner, polish it, and keep an eye on it for a week or so, to see if that helps? Sounds like the car is performing as expected, mechanically, so that would be my first port of call.

only had the car a few weeks and three weeks ago gave it a bloody good clean. Wash, rinse, wash, wax, glass conditioner - all autoglym. No t-cut or anything like that. Am intending to give another good clean but the car was squeeky clean

Okeydokes. It was a long shot, I guess.

We've had dry/windy weather lately after a lot of wet. It'll just be dust from the road raising its head.

My motorbike was always the same after a short shower. Greased up like buggery, lots of rain was always cleaner.

Mine gets really dirty on the back end too - most noticeable at the rear of the wheel arches and around towards the bumper. As Alex said, it's worse during a dry spell, when there's lots of water around on the roads it's muddier less sticky dirt.

Get some AC50 sprayed on anything you want to keep clean. I used to use it on my motorbike exhaust and it kept it mega clean. Don't get it on the paintwork though