need help supra over heat

[91_7mgte]

hi, i'm new to supra forums and i just got my 91 supra but i't is over heating. i don't know why it's overheating. i have replace the waterpump, thermostat so i think it's the fan clutch. well this is how the car overheat. the only time it well overheat is when it's on the freeway go 70 to 80 mph. the reserve tank would be full of hot coolant and when you take off the cap there would be steam and every morning when i start the car i can hear water running behind the dashboard. anybody know what wrong with the car.

[joel w]

Is it loosing coolant? It sounds like a blown head gasket and the exhaust may be entering the coolant system? It could be a few things. Sorry to be the bad news guy..

They sell a kit that detects exhaust gasses in the coolant that might be worth picking one up.

Take a read though this thread.
http://www.toyota-supra.info/forums/mkiii-faq/13-help-my-car-is-overheating.html

[theWeezL]

often overlooked item is the radiator cap...they are designed to maintain pressure to a certain point, then open up to relieve the pressure if it gets to high. If its old and weak it can actually not hold any pressure therefore allowing your coolant to boil and overflow. Its also like a 5 dollar part and worth trying

[joel w]

^^^Good call, I assumed that was in the link but i do not see it..

[1988gte]

my cap had the gasket torn and cracked never lost water or heating problems after the replacement cap

[ddmcse]

you better hope it's the cap and get one from toyota not a parts store
you might pay 7-8 bucks more from toyota but spring for it .

the water rushing sound in the morning is from the lack of the proper water level

get the new cap , top off the coolant , i would park the car on a serious incline to try and get any and all air out of the coolant system .
if you lose more water and hear the rush again you have a BHG