I drain the rad in the S4 (88 vert) and was burping it, found that the rubber in the flat cap (rad fill thinggy, beside the alt) was REALLY brittle,

Questions Gentlemen/women:
1. Do I need a new one?
2. Can just replace the rubber? where can I get it if yes?
3. any aftermarket source? or do I have to run to the stealership?

side question:
after I burp the system, I will have to top off at the flat cap?

thanks,

 

flat cap = rad cap???

Yes, its very important - get a new one......I recommend using an OE cap, but if you feel like cheaping out autozone should have one.

 

bah...it's just a flat cap...get one from autozone for a few bucks. If you need to replace the pressure cap on the filler neck, you need to make sure you get one that is the same pressure rating. I think it's .9 Bar

 

nope, the flat cap is the one behind the rad, it has no pressure spring mechanism,

in S4s this is supposed to the one used to burp the system.

 

you can put a regular pressure cap up there with no ill side effects, most auto parts stores do not carry "flat caps"