This is my first post here but this is Toyota wheeler #5 for me. I just got this 90 extended cab that was bone stock and in great condition. The motor had been gone through just a few thousand miles before I bought it from a friend. When i bought the truck it didnt have a thermostat in it at all so I replaced the thermostat with one from napa and it over heated right away. I checked to make sure it was in right and it was. Then tried a Toyota thermostat same thing. Long story short I wound up drilling a 1/4" hole on the thermostat to let some water through and that helped a ton but it would still get hot. I have flushed the system for hours on end and blown out every hose I can get my air nozzle on. New fan, new fan clutch, new shroud, new radiator, new hoses. If i drive aroud town it the needle on the dummy guage stays straight up and down but if I am cruising down the highway and start climbing up hills the temp climbs up to almost the red. I can wheel all day on the trails and not heat up and when i am coasting back down the mountian it goes ice cold? i have also had a sniffer put on the cooling system to make sure there are no exhuast gasses in the cooling system. I will check the timing today but any ideas?


http://i173.photobucket.com/albums/w...7/IMAG0030.jpg

 

wth? why is it overheading (I know that is why you posted.. I have no clue.)..

 

Really no ideas?

 

maybe a gunked up water pump or a radiator cap. I think you have everything else about covered.

 

it has to be something internal like the water pump or something stuck in the water jackets??? so weird.

 

Maybe a stupid question but has it been bled properly?

 

It has a new water pump, new radiator cap, compression checked, and I have done every trick i know to bleed the cooling system. any more ideas?

 

It gets to the red on the idiot guage before I shut her down. It doesn't use any coolant and the fan clutch is brand new. It will heat up going down the highway at 65 pulling a hill but not heat up 4wheelin in the snow???

 

change your temp sensor

 

temp senser or jackets plugged??

 

i'm positive its the temp sensor think about it he has a thermostat install and his motor goes from hot to cold just by going down hill

 

He said that was new.

 

My buddy that I go the truck from said his dad put in the water pump so I am halfway thinking about pulling it out and throwing a new one in just to see if there could possibly be something going on in there. I guess while im at it i should probably get a new temp sensor and a real gauge. Does anyone have a good link to a water pump r&r thread ?

 

What engine does it have?

 

3.slow

 

Here's the FSM for a 93 truck: http://personal.utulsa.edu/~nathan-b...fsm/index.html

The timing belt has to come off to replace the WP, did the PO put a new timing belt on?

Might try taking off the winch and try that (it blocks air flow to the rad). I've made mine removeable now, only takes about 10 mins to install it. I carry it in the tool box if I need it. Does running with the heater full blast help?

 

I read somewhere on here that there are two temp sensors, one for the gauge and one for the ECU. But that maybe was for the 22R. Check the FSM for your motor.

I would get a temp gun or maybe even a thermometer and see what the actual coolant temp is. If your upper hose is between 180-210* when the gauge is pegged, then your gauge sensor could be bad.

 

Nice lookin' truck by the way

 

I had an almost identical problem in my '85, would only overheat at speeds over 65 and that was due to a partially clogged radiator. Would cool fine at slow speed, wheeling, etc. But at high speed/RPM with high coolant flow rates, the radiator flow would likely become turbulent and drop in efficiency. Interesting that if I were going up hill in a lower gear/higher RPM, and the temp started to rise, I could shift up to a higher gear/lower RPM and the temps. would drop.

 

Did your issue ever get resolved?

I am having a simmilar issue. Runs fine for 20 minutes then gets hot as I accelerate. Coast and the temp comes down to normal. My rad is a year and a half old I hope it is not clogged. Heat blows hot. Top rad hose is soft and really hot. Could it be collapsing with increased speed of water pump?