My stock radiator does not have a cap on it. The cap is on the thermostat housing on the engine. The overflow taps into the same place.

My buddy Ian (Molotovman) has a Koyo on his Turbo II. That, and the stock S5 radiator it replaced have that long gooseneck filler which looks like an accident waiting to happen. (Looks easy to drop something onto or lean on and break.)


Do all aftermarket radiators have that gooseneck?

I'd prefer a radiator without a cap entirely. It'd just add more points to leak.

If I MUST get an aftermarket radiator with a cap, is there a filler neck without the overflow attachment? I hate the look of a capped off line there and it'd be less points to leak at.

 

The Koyo made for an S4 has the extra fill location directly on top of the tank, rather than on a neck extending out. I actually just cut the thing off and had a plate welded over the hole, since I too have my filler on the thermostat cover.

 

Yeah I really don't get the two filler holes thing, I imagine there is a reason for it, but it just seems redundant.

 

It's so they can sell the same rad to both S4 and S5, turbo or NA owners.
The S5 NA doesn't have provision for a rad cap at the thermostat neck, so it needs one on the radiator itself.

 

And so that you can burp the cooling system and bleed all the air out when filling it. I forgot there's that screw on the side of the upper hose barb on the stock S4.

 

Apparently some stock S4 radiators came with the filler directly on them, just like the S4 Koyo & similar to S5s (minus the goose neck). They came from the factory with two radiator caps, but the overflow port is blocked off on the thermostat neck. The plastic piece under the thermostat cover's cap is actually molded with a nipple, but it's sealed off. I had never seen it up until a few months ago in another thread, where a bunch of S4 owners posted pictures of their stock setup. I would assume that these weird S4s are the reason for the filler on the S4 Koyo.

 

^ True that, there are many variations of the S4...

Like my early one. It's got the coolant reservoir over near the leading coil. I've got a lot of hose from the thermostat neck, around the intake air plenum, over around the fan shroud, and to the reservoir.

 

I have two fill caps because I'm 2x cooler