Boyakasha

iTrader: (2)

I bought one of these a while ago and replaced the current rad cap, then I saw a pic of someones STi and they had it on the coolant reservoir.

So the question is do both caps need to be replaced, do you only need to replace the rad cap or do you replace the coolant reservoir cap?

SL_WRX

Good question - I imagine only the rad cap. Also while they do look nicer do they actually help/improve performance in any way ??

Boyakasha

iTrader: (2)

Another good question. I am led to believe that they raise the boiling point of the coolant, but this is only relevant if your coolant is getting to that point which it shouldn't be if the car is running properly. Makes me wonder why I bought it

Oh that's right I am an engine bay tart

Boyakasha

iTrader: (2)

I guess nobody actually knows the answer to this then.

SamUK

iTrader: (1)

Always thought it was for looks...thats why never bought one...

john banks

I'm using a 1.3 bar STi one now to raise the BP of the coolant, to reduce the chance of headgaskets leaks at higher boost.

Boyakasha

iTrader: (2)

John did you put it on the radiator or the coolant reservoir.

john banks

Coolant reservoir, new ages are different and have two caps IIRC?

Boyakasha

iTrader: (2)

Cheers John, Looks like I'll have to get another cap.

john banks

I don't know, check with someone that knows about the new cars.

JIM THEO

John is correct, new age cars have two caps, change only the coolant reservoir cap with the STI one the other is higher pressure!
JIM

Boyakasha

iTrader: (2)

Thanks Jim, I finally have the answer

Engineer@Uni

I think theyre supposed to go on the rad. We had a high-pressure cap on the rad of our student formula team in university, and they do raise the boiling point because of the stronger spring they have. But as stated, they shouldn't be needed unless you intend to really push it hard. Personally I think they just look nice. I don't think they'll give that much of a difference in Subarus unless you drive them in a really tight track with speeds to slow to get the radiator convecting correctly.