i have a 99 4runner sr5 v6 and ive notcied some wierd overheating problems. one day when i was just drivin, i noticed that my temp gauge was redlined. no steam, and running fine. i got home and sprayed everything off to cool it down. then started her up and drove her again and the temp on the gauge stayed normal. this happened a couple times and i repeated the process. and when lookin at my rig more. i noticed the return tube for the coolant was really hot, and the feed tube from the radiator at the bottom was cold. so immediatly i thought my thermostat was stuck closed and sticking. so today i spent 2 hours putting a new thermostat in. after all said and done i took her out for a drive, and what do you know!? the gauge skyrockets again, but still drove fine and no steam. and when i checked the hoses again and the return was hot and feed like barely warm. so im wondering what is causing this problem. maybe just my engine temp gauge is malfunctioning? i just dont know what it is. any ideas of what it might possibly be?

 

Is your tranny fluid low? I ran mine really low for awhile and it was overheating really bad. Course idk if it's different with a 3rd gen or not. Just throwing a random idea out there...

 

how is your quality of coolant..

and usually when it sky rockets like that you may want to ensure that your fan clutch is working correctly..

and you may also have bad head gasket..

or a clogg some where a.. good garden hose flush is always a must.. so make sure you use your neighbors drive way when your doing this, no need to allow coolant to run all over your driveway..

 

Are you burning or leaking coolant? Did you replace the hoses/clamps when you replaced the t-stat? and x2 on the fan clutch, do you hear a "roar" when you start the engine cold? Could also be the water pump...

 

When does it actually overheat? When driving slow around town, or above 40 or so? If it overheats when driving slow but not at speed it's likely a fan clutch. If at speed it could be a radiator that isn't up to task any more. You might have an air pocket in the cooling system too. I've never had this problem with a Toyota truck, but I have on older MR2's and a few BMW's I've had. Usually to combat that I crack the heat to full hot and run the engine while topping off the coolant. And of course you are using a 50/50 mix of antifreeze and distilled water right?

 

try burping the cooling system, if not look if yu have a bad head gasket or if your water on a hot engine mite have warped your head letting in or out a small leak. i had the same after my rebuild. thers 6 cylinders, six ways to seat your gaskets i chose the wrong way the first time around. runs beautiful noww. cocnlusion from me and my mechanic