Strange Cooling System

[russ35]

No I'm not asking where the pressure cap goes :laugh:

Bought the S3 in the middle of August. Realised earlier that I haven't checked the water level since getting it, so take of the pressure cap from the swirl tank to discover that it's only a plain cap. The other thing I should mention is that the previous owner replaced the original overflow bottle with the one that would normally be fitted with the engine (something like a 2l instead of the 1 litre TVR fitted). This bottle has a normal screw top. So I don't have a pressure cap on the system!!! Oh, and the small overflow pipe from the bottle appears to have a bolt or something stuck in the end of it. So I appear to have a totally enclosed system!!. I've had no overheating problems or anything.

I still have the original bottle in the bits and pieces that came with the car, found this and it had the pressure cap on it. Was going to fit this but then noticed that something didn't look right with the pipes on the swirl tank. The top pipe from the swirl tank (the one that is above the seal point if the pressure cap fitted) I would have expected to go to the overflow bottle, but it doesn't, that is the next pipe down. Going from the picture in the bible (p. 149) it should be the top of the swirl tank pipe. Can anybody confirm this from their car?

So plan of action is (I think)
Swap the two top pipes around so the expansion bottle pipe is at the top.
Fit pressure cap to swirl tank
Remove bolt or what ever from the end of the overflow pipe

I'm going to leave the bottle as it is on the nearside wheel arch, so oil filter is easy to reach now.

I hope this makes sense, I just cannot see what/where this all happened - I suppose that is the risk if you buy from somebody who self services.

Russ

[Hoover33]

Ohhh dear....... you've just started the great debate on where the pressure cap goes again.

Leave it on the expansion tank

[S3Paulo]

My pressure cap is a long reach cap fitted on the swirl tank...and guess what....it works a treat...no over heating....no water loss.

...Paul

[GreenV8S]

Having trouble working out what the connections are in your system, but one thing's for sure: you don't want a completely sealed system. The gas bleed is going to build up pressure until it leaks somewhere, so you need to ensure it does have somewhere safe to bleed from. Is it possible that the screw cap you refer to is a pressure cap? Not all pressure caps use bayonet fittings. If this is a standard production header tank it is quite likely that it was originally fitted with a pressure cap.

[russ35]

Just been and had a closer look at the overflow bottle screw top (now there is some daylight). It does appear to have some sort of pressure thing in the cap.

So I think I'll leave alone, this setup worked for the previous owner and it has given me no problems to date.