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hello i ve got a h2 which has got a overheating proble, as in coolent boils out of the expansion bottle.it only seems to do it when its been ridden hard and then when im slowing down it will over heat i.e on a track day,it was fine during the 20 minute session and on the slow down lap but as soon as i came into the paddocks it started to boil up.
the fans cut in fine its always had the correct amount of coolent and today had the thermostat replaced (at a fair cost) but i took ot for a little test and sure enough as i pulled into my drive it boiled over. now in thinking that maybe there could be a problem with the water pump/circulation? i was concerned that maybe the head gasket may have gone but the oil doesnt look to bad and its not smoking etc
i would be very gratefull for any advice,cheers tom.

get a compression test done, this should help give you some indication as to the head gasket or not.

Also worth checking the rad cap too, what does the temp gauge say?

the temp gage sits when boiling over just under half way up the gage

Yeppers, the head has blown mate.

Bubbles are from the cooling system getting pressurised.

oe head gasket is cheap from cradely kwakers.

mine was doing the same - kept coolish aty 90 on mway, but was overheating by the time i'd stopped at petrol pump.