7mgte overheating problem

[87boosted]

I recently bought a 87 supra with the 7mgte. ive been driving the car for a little over a month with no problems. About a week ago it started running warm when its sitting. As long as the car is moving the temp stays normal but when you stop it starts climbing. Ive read a lot about the dreaded blown head gasket problem and I just wanted some advice before I try to replace it. I'm not sure if the head gasket is the problem, ive checked the oil and it doesn't look milky. I have also replaced the radiator and when I drained the old coolant it was pretty clean. was just wondering if it may be something other than the headgasket. Any advice would be greatly appreciated! thanks!

[Bru]

Check the coolant level to be sure that its not low in the radiator and that the overflow tank functions normally. That is, the level increases slightly when it's warm and then gets drawn back when it's cold. There are high and low cold lines on the tank. Does the radiator still have the plastic fan shroud or is that missing? It would be more necessary for cooling at low engine speeds than high. There's even a small section that clips on to the bottom that took me years to find. Sometimes air can get trapped in the system. The way to burp it is to run the engine on an incline with the front high and the heater on. The classic sign of a bad head gasket is after running the engine that you get a lot of gurgling from the overflow tank that can overflow coolant onto the ground. Be sure you're using at least 50/50 antifreeze /distilled water or a premix of the same type. Check the fan clutch when it's cold by pushing on one of the blades with a little force. It shouldn't turn more than 1/4 of a turn. When the engine is warmed up and you rev it, the fan speed should increase with the speed of the engine. It might not be a bad idea to check the function of the thermostat by putting it in hot water or replace it. The jiggle valve goes up and don't over tighten the two retaining bolts. They strip easily. I use a small amount silicone on the flange. Check the tension on the fan belt. It also runs the alternator. When it's loose, it usually squeals on startup. Does your auxiliary fan kick in when it's hot? The only other weirdness I can think of is you may have an aftermarket water pump with stamped steel impeller blades that have rusted off. The OEM water pump should have AISIN cast into it on the front. That one has a cast-iron heavy-duty impeller.

[MikeC]

Just had the head gasket replaced still over heating can anyone help with issue? Just replaced the thermostat this morning didn't help. Does make a gurgling sound.

[Bru]

Be sure the thermostat is installed with the spring portion going into the thermostat housing away from the hose. When it's cold take the radiator cap off and check that the cores are not plugged up. Another problem is that leaves get sucked up between the front of the radiator and behind the air-conditioning radiator. If you take off the two retaining straps you can tip the radiator back just enough to peek down in there with the flashlight. It might be a good idea to take the radiator out and back flush it and clean the fins between the cores. After this is done and you run the engine and it still overheats you might have head gasket problems. The classic symptom is that the overflow tank gurgles fills up and overflows onto the ground. Are sure you didn't leave any paper towels or rags in any of the coolant passages when you put it back together?

[MikeC]

Thanks for the information Bru. I'll look at the radiator.