Fo by Fo

Hey my v6 91 4 runner overheated on me the other day, so I figured it might be the thermostat. I boiled it to see if it opened and everything checked out fine. Confused, I decided to just buy a new thermostat anyways, but that didnt solve the problem, still overheating, so I just pulled it out and have been running fine for the last week or 2 with no thermostat. Any Ideas of what it could be? I was thinking maybe a water pump?
Thanks

rdharper

Any coolant loss, now that you are controlling the heating?

Fo by Fo

No, i just put water in but the level has been fine.

rdharper

Well, if its not losing coolant, then a couple of other possibilities come to mind.

1. Exhaust into the cooling... look for oil in the radiator/coolant.
2. Water not circulating. I believe you said that if you remove the thermostat, you *never* overheat, right? If true, of course, that implies you are circulation adequate water.
3. Water circulating, but radiator is not fully cooling due to some blocked passage.
4. Maybe fan/clutch not kicking in properly.

If you can exclude all of the above, maybe someone else has an idea.

mtnfreak

How's the fan? Is it pulling air through? Try a search, there are a ton of ideas on how to check it. Try spraying out the core with a garden hose - too much mud / dust / leaves, etc will restrict the airflow. Any oil in the coolant? Anything abnormal on the underside of the oil cap? If you have to replace, don't F around with anyone else - go straight to performanceradiator.com.

Fo by Fo

I idled the engine for about 5 min. then shut it off and the fan kept spinning so I think its the fan clutch. I got one just need to install it.

Fo by Fo

If my fan clutch was bad, wouldnt that mean the fan wouldn't spin? Cause my fan still spins when the engine is running

kdawghuntnfish

I am having the same problem. So far I have ruled out the thermostat. I will be having the radiator checked tomorrow. Your fan cluch could be slipping. Try to spin it with the engine off, but warm. If it spins freely it may be slipping. Also, if you notice any oil around the fan clutch it is bad. You can also check the play. Wiggle it and see if there is alot of play in the bearing in the clutch. If your fan has the infamous ring around it like of these trucks, it is hard on the fan clutch becaus of the xtra weight. Here is the link of the post i have been working on to troubleshoot the problem. Good Luck!!!!! https://www.yotatech.com/forums/f116/new-thermostat-bad-radiator-blockage-88604/

Johnny TTT

I'm having the same problem. Installed a new thermostat from toyota and a new rad cap. The truck works fine with no thermostat and circulates but just pressures up and gets hot when the thermostat is installed. The water pump is good. I changes it out to make sure.

Any thoughts

bradbarber

I'm having a kind of the same issue, around town it seems to be running right at its normal temp, but once i'm on the freeway for an extended period of time it starts to really heat up almost to the red line any suggestions?

RERunner

I was having an overheating problem with the thermostat in, but when it was out the truck ran OK. I replaced the radiator, checked the thermostat (opened at 180), and changed the fan clutch. Turned out to be the head gaskets. Last idiot put the left one on the right side which blocked a coolant hole. It was a pain in the ass but everything is running great now...