Make sure your radiator is in perfect condition, with no cooling fins rotted and no signs of leaks (these will show up as blue/green/white) snail trails down the side, or blue colouration from the radiator core itself. Always replace faulty radiators, and flush out the heater matrix radiator. Also, beware blocked radiators, these are often ones that leak, but that no longer leak generally because they have been filled up with cheap fix fluids that block everything and are not wanted in your engine.