water pressure/black smoke

Hi got a 1999 t reg 1.9 turbo scudo when accelerating hard blows black smoke also when driving the pressure in the header tank gets excesive there is no loss of power or signs of water in oil.Is it most likely to be the head gasket or somthing easier to rectify..

still got the water problem seems to be ok round town but on a long run it forces water out of the header tank put new cap on still the same .gets to temp thermostat opens and all pipes are within 1 degree of temp all around the engine so ruling out the waterpump it is realy doing my head in please help...radiator is clear and fans work at the right temp...

It sounds like you have a built up off pressure if the coolant is forces out of the cap. Does it overheat or as it be for?

no it does not overheat and never has ive done a block test and the head gasket is ok...

You HAVE got the right water level in the header tank right? It's not meant to be full to the top when cold.

When cold, the water level should be somewhere near the bottom of the tank (a line on the tank shows it). This leaves room for expansion (as water does when it gets hot).

yes water is ok .around town no problem but on a run it pressurises and leaks out of the filler cap put new cap on ..after some time the warning light comes on for low water.and needs topping up no white smoke and no sludge in oil .

air lock in the water system maybe?