What's up yall I'm new in here so any. I've got a 92 toyota with 250k miles 2wd 5spd 22re p/u. The problem I'm having is that in the morning while my motor is still cool, everything works fine. But if you turn the heater control on before the motor comes up to temp. the truck will began to run hot. You can watch the temp. gauge for it and when it starts to get about half way turn the heater control and temp off for about 1 min and the back on and the temp will regulate and work fine. Now if you start off in the morning without the heat on the truck will never come close to running hot. Or if you wait until the motor comes up to temp and then turn on the heat it's fine. Like I said it's just when the motor is cold and you start off with the heat on it will warm up on you. I'm just a shadetree mech so I'm in need , help me please.

replace your heater core

Not doubting you but is that by experience, educated guess or have you run across this problem before?

happened to me in my wife's old pontiac sunbird, and in my old 89 ford ranger. so, yes it's from experience. not with toyota's but general experience i guess. but having said that, I'd probably spend the 5 dollars on a new thermostat just in case. If that's the problem (it could be but from your description it's prob not) it'd be a cheaper fix. IF that doesn't work, remove the heater core and replace it. They run anywhere from 50 - 100 dollars, but if there's a radiator shop nearby, you can have it repaired for much less. Hope this helps.

Well it wan't the thermostat so I guess I'll have to try something else

Removing the heater core is a big job. You have to pull the dash back.

There's only a couple failure modes for heater cores that I know of:
a. leak
b. blocked

If there's a leak you will smell it and have moisture on the inside of the windows even with the blower at max.

If it's blocked you won't get any (or very much) heat.

Either failure would not affect the engine temp or should be of concern.

Maybe there's a learning lesson here for me....who knows. But my question is: Do you get good heat from your heater core ?

Yeah the heat works fine. Like I had a guy tell me yesterday, if the heater core had some type of blockage it should be having problems all the time. I don't have a clue. I've talked to radiator shops and some import mechanics, they all say they've never heard of anything like this ever happening.

Well maybe all the wondering is over, I might have solved my problem. I replaced the heater control valve and haven't had anymore problems yet. So hopefully that's going to resolve the issue I was having. Thanks for everyone's input on the problem.

hi. wondering how eveything is going with your overheating prob. still workin good since you repalced the heater control valve?

everything is still working fine. I just can't understand how in the world that valve can make it run hot .