I've got a heavily modified 626 with a kl-ze powerplant. The radiator popped right afterI got it. Its got one from the junkyard now. does fine with the heat on but I live in Ga, and it gets too hot for all that. Btw.. already replaced upper and lower radiator hoses too. this car is a lot of trouble[&o]

 

haha i hear you, mine used to have the same problem but a relatively cheap and simple solution, when the engine heats up thecoolant heats, when that happens your cars thermostat opens up to let in fresh coolant and keep the engine cool, if the thermostat gets stuck closed or open your not circulating fresh coolant and it heats very quickly, if you turn on the heat its like venting all the built up heat out of the engine, into the cab and out the windows but like you said in GA, its too darn hot for that so long story short, pick up a new thermostat, you can get it for like $4.99 at napa and its very easy to change :-)

 

that or you need a coolant system flush look at your antifreeze and see if it is green or looks lik pound water either way a eazy fix