right my mums car is having abit of trouble as it seems to over heat abit as she describes, the RED light came on once and she stopped to car to let it cool down, but recently its been having trouble starting and the heaters seem to work warm and then turns cold after 5-10mins, and pressure seems to build up, if i was to take the radiator cap off it will gush out, also can smell abit of fumes or something if i was to take oil lid of and put my nose to it 
could the thermo stat cause the heater problems going cold and make the rad water get pressure rised or is it the dreading head gasket going going GONE

thanks adam19
could the thermo stat cause the heater problems going cold and make the rad water get pressure rised or is it the dreading head gasket going going GONE
thanks adam19