rover 25 1.6 16v boiling up???

hi all,have a problem and wondered if anyone can help?



its a rover 25 1.6 16v

when ticking over it seems fine,get up to temp and fan kicks in and out etc,but when taken for a drive it seems the water fills up the expansion bottle and overflows (cap on)

its already had a head gasket (by previous owner approx 10k ago)

ive changed the thermostat,and fitted a new gasket to inlet manifold,had new radiator also.

just cant understand why its ok for an hour just ticking over,but after about 10-15mins of driving it goes on one??(ps also had a sniff test to confirm its not the head gasket again)

so im stumped!,doesnt appear to have any airlocks,heater gets hot etc.

im confused .com ,can anyone help....please!



thanks

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