Suspected Aux Rad Leak

[adsgreen]

Aux rad is just what it sounds like - a secondary rad for the coolant circuit. The rs4 has two aux rads one each side.
The aux rads are thermostat controlled so coolant will only flow through them at a certain level. Hence why you only get steam under high temp conditions.

However, whilst the thermostat is open:
- you will be losing coolant
- the pressure controlled environment of the coolant circuit will be compromised. As such te boiling point of the coolant will be dramatically cooler (around 100c) which will cause air bubbles in the system which dramatically reduces the coolant efficiency. When the system is working properly the system is pressurised and this raises the boiling point to around 120 degrees.

It's not really a problem you can leave and expect no problems with even assuming you keep topping the coolant up.

In terms if what it's used for, I would suspect it is mainly for extended auto bahn and track work. 99.9% of uk drivers won't ever stress the system and given supercharged systems run considerably more power with one rad I don't see it as a problem.

[rugbybloke]

Thanks Ads, will get the leak checked out in the new year.

[Stairs]

Thanks very much, great info...

[Stairs]

Update for everyone...

I took the car to Nirro (in East London) They had a good look over it and found that the Aux rad was indeed leaking. I called the used car dealer I had bought the car off and explained the issue, he said "well thats not covered in the warranty, the best i'll do is you pay for the part and i'll fit it". So I pointed out the 'sale of goods act' and low and behold he changed it all for free, actually a nice guy to deal with, just not an audi specialist I guess.

Anyway, thank you for all the advise and help, I hope it is the last time I need everyones help, but I fear it won't be...

Oh yeah, 420hp, snow on the roads and turn off the traction control = Fun, even if a little worrying.

[MikeFish]

Glad you got it sorted. By the way, it's 414bhp not 420. It is 420PS.

[Stairs]

..... 414..... Still more than any of my friends cars.... which is all thats important in this world!

[MikeFish]

..... 414..... Still more than any of my friends cars.... which is all thats important in this world!

Very true!