davey, how hot is hot, the water should be warm, as the water is taking the heat away from the engine, if it is boiling hot then there is either not enough flow, do you have a good jet of water coming out the "pee hole" to take the engine heat away or the engine is getting too hot, most engines however will should shut off before you blow anything, unless your engine is really old, or give a waring buzz if the engine is getting hot, thats if it is fitted with a warning buzzer.