hey i got 2 cents for ya, for checking the defroster. its tedious but use a razor blade to cut the tint off just over the elements and peal off the little strip so you can expose the elements and test them, and the fans .. the big one behind the radiator is your main fan for the radiator the smaller one in front of the radiator is for your AC system, im not sure how the dohc is but on the sohc when your timming belt starts to stretch or your tentioner gets week, the water pump starts to slip and not work, or if you got any oil on that belt some how it will slip on the water pump, something to check, when its overheating, is the heater still blowing hot air? if its not then your coolant isnt moving through the radiator or the heater core and your water pump isnt working for what ever reason