[Moog]

Hi Rich - Thanks for answering. I'm thinking and hoping it is just the cap, but am slightly nervous that there might be something else wrong.

Temps - The standard thermostat on a WBX starts to open at 87°c and is fully open at 105°c. I actually have a VR6 stat which starts at 80°c and is fully open at 100°c, so with normal water operating temps at 90-95°c then i figured this is fine. My choice of rad location probably does make it run a bit hotter than if i used a front mounted rad, but i don't think that it is getting too hot for the engine or system to take. I have the ECU controlling the fan - cuts in at 105°c and cuts out at 95°c. (All temps are measured at coolant outlet from the engine, so at the hottest part of the system before the coolant has gone though the rad). If i recall, the Mk2 GTI ran quite hot like this as well, so the tank should take it if the cap is working properly. Maybe i'll trim the fan operating temps down a bit as well and see how it goes.

I have found out the Golf Cap is rated at 1.2-1.5bar, while the T25 cap is 0.9-1.15bar, so will try a T25 cap with spout and an additional non-pressurised overflow/filler tank as per T25 and see if this works.

Heater matrix is a std T25 auxilliary heater under the rear seat - takes an outlet from the left head and returns into the top of the water pump (T'd into the hose from the header tank to water pump) so similar to T25 setup.

I did think it may be to do with the overall coolant volume being too small, but the standard Golf Mk2 GTi is listed as 6.5 litres coolant volume (smaller than i thought), and i have about the same.

New bottles & caps coming Monday, so i have to just sit and wait until then - very frustrating... still, at least i might get some more plastering done in the kitchen...

Ta

Moog