First off, I've got a '99 4Runner with the 3.4. When idling in the fast food line, the temp needle rises into the red after a couple of minutes. But as soon as I get back on the road, it drops to the correct level in the middle. My brother's Taco with the same engine does this as well. Anyone have any ideas why this is happening?

 

It sounds like either the thermostat that controls your fan or your fan itself is out. I'd change the thermostat to see if that fixes it and then move on to check the fan motor.

 

The thermo was replaced not long ago. Which fan are you referring to? Can I look for it while it's idling? Thanks, TotaNewbie

 

i know the 3.4 doesn't have an electric fan from the factory, but this happened to my '90 lumina back in the day. turned out that the electric fan motors, both of them, were toast. i guess i would check threads about overheating and see what is suggested. thermostat, radiator, coolant, fans, hoses, hopefully not anything major. good luck.

 

Even new thermostats can be defective. Or maybe it wasn't installed right. Take that thermostat back and tell them it's defective. See if that takes care of the problem.

 

Thanks cackalak han and pattycakes77. I'm trying to figure this out on the driveway first. If I can't figure it out, I'll take it to the mechanic who installed the thermo.

 

My guess is the fan clutch is bad. Is your fan shroud ok?

 

How can I tell if the fan clutch is the culprit? The fan speed is noticeably slower when idling. I'll check the fan shroud.

Thanks.

 

Obvious Questions, but are you low on coolant? That will cause it in a heartbeat as well...If not, then I would guess fan clutch,thermostat, or plugged up radiator.

 

That's a good question, I've never seen anything in the FSM about a testing proceedure. Found this on google:
http://www.popularmechanics.com/how_...e/1772922.html

 

Sounds like a clutch fan to me as well.This is assuming the shroud is intact and there is no debris inbetween the condenser and radiator.A quick check is with the engine is cold grab the fan and spin it,warm the enging up to operating temp,shut enging off and then spin it.It should be very hard to spin,if it feels just like it did cold,its bad.


Rules of thumb for coolant systems:
thermostat stuck closed would cause an overheat almost immediatly.thermostat stuck open would cause lower than normal temp and weak heat.Low coolant will cause boilovers and gurgling sounds from heater core.Radiator clogged will overheat while driving not when at rest.clutch fan bad will cause overheating at rest not while driving.

 

Good to know. I tried spinning the fan with the engine cold. It's tough to spin when cold.

 

The fan clutch is filled with a sillicone fluid. It might need changed. The dealer sells fluid or you can use hobby grade shock oil from a RC car at a hobby shop. Theres a thread on here discussing this, do a search.

 

Cool, that sounds like a cheap thing to try.

 

Could possibly be the coolant temp. sensor.

 

same thing would happen to me. here in hawaii, when hitting the trails, the mud is like shrink wrap. if you wheel your runner, i would power wash the radiator. i did this and tons of crap came off the veins and now it is back to normal. i am with you...start easy then spend some money. hope it works.

 

fireteacher is correct, power wash the crap out of the radiator I know the 2 of you have been playing in the mud....

 

Be careful not to bend the cooling fins over if you power wash the radiator.