Remove the hoses and thermostat housing and unbolt the thermostat housing from the head. Give the sections where the hoses connect to a good clean and hit it with a wire brush on the end of a drill (WEAR SAFETY GLASSES WHEN DOING IT AS THE WIRES FLY OFF THOSE THINGS LIKE FLYING NEEDLES - YOU DONT WANT TO GET ONE IN THE EYE!). Once all the loose **** is removed look for severe corrosion that may have caused holes right through the piping. The alloy corrosion will stop you from getting a good seal so remove as much as you can and/or replace the thermostat housing cover.
