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I'm looking for some help with the aux rads on the RS4 Avant...

What are the tell-tale signs when they go?
Is it always the passenger side one that fails?
Has anyone made a guide on how to change the rads?
Where is the best place to buy a replacement rad?

Thanks in advance

Both of mine went . Drivers side first then the passenger side about a year later . You can swap them from side to side if you want to do a cold air feed on the drivers side .
I brought mine from RPS online . Imho it's not worth getting s/h ones as they are going for about £150 whereas you can buy a new one for about £220.
Guide on here to fitting a cold air feed which involves removing drivers side aux rad .
Tell tale signs look through the fog light grill and you will see pink crusted rad . Mine had a puff of steam coming out on parking up .

Got both aux rads refurbed at northern radiators in leeds,total cost was £90 plus vat and only took two days.
May be worth looking for someone in your area

I used to keep them clean and never really noticed the classic signs - it was howver obvious really as my coolant needed topping up and of course now it doesn't. I probably had them replaced sooner than strictly necessary but didn't want to risk a failure.

Not sure if this helps, I replaced my drivers side aux rad. As stated above, just get a new Audi one (they sometimes come up on eBay).

viewtopic.php?f=35&t=127791&p=878335#p878335

Not too bad a job, but quite fiddly access and of course the bumper has to come off.

Thank you for all the responses, especially the fitting guide.