Engine overheats in Bighorn 3.1 (4JG2T)

[Bikedude]

Hi. Muy Bighorn overheats going up hills when towing a trailer . Never used to do that. I have flushed the radiator but didnt seem to make much difference. I intend to change the thermostat hoping this will help. I have noticed the transmission gets really hot too, and locks in third gear when hot. Obviously I need a trannie flush and oil cooler fitted. Would the transmission heat up the water temp that much? Also I have been told I need a new Throttle Position Sensor at about $4000 dollars. Does that sound right and does anyone know of a fix?

[geeves]

What year and is this the electronic controlled engine?
Main culprits for overheating in no particular order are
Radiator This has been flushed but if yo use off road it could be blocked on the outside. Also if its been neglected it might need a professional clean.
Auto trans. A faulty trans will easily overheat an engine as they effectively share the same coolant. For towing on any auto an extra cooler is a must.
Injection timing. If this is out or has been played with for more power it can cause overheating.
Specific to your engine
Cracked head causing coolant loss leading to overheating
If electronic faulty injection pump giveing incorrect fuel settings. This one can kill the engine very quickly.
I would be checking wreckers for the TPS or giveing it a good clean before condemning it at that price

[isuzumudman]

Check your viscous fan too! The easiest way to prove it is working properly is to stop the vehicle and switch off the engine when the engine is hot. Lift the bonnet and attempt to spin the fan blades by hand. If the fan just about free-wheels when hot then your viscous fan is stuffed. The theory is that the viscosity should increase with heat making it harder to turn by hand. Be warned, a mate tried 2 new Chinese ones from Ripco before getting a good used one from a wrecker. Made by Aisin and are also used on some Toyotas and Nissans.

[isuzumudman]

As far is your TPS is concerned, $4,000 you gotta be kidding. The TPS on your vehicle is located on the top of the injection pump and is fixed with 2 screws. There are 3 wires leading to a plug. The centre wire is the potentiometer wiper and the other two are each end of the potentiometer itself. To check it I mark the position and remove it. Connect an ohm meter between the wiper and one of the potentiometer wires. Maximum resistance should be about 4.8 ohms and minimum should be really low like 0. Starting at one extreme turn the wiper very slowly to the other extreme. If the resistance fluctuates or rises sharply at any point then the unit is stuffed. You should be able to get one from a wrecker for under $100 but you must check it first. If you can, get one off a manual bighorn as they are fitted to the pump but are not actually connected to anything. Finally, the adjustment is the more anti-clockwise you turn it the less sensitive the kick down will be.
Have fun.

[Bikedude]

Thanks guys. That was really helpful. I guess I know what Ill be doing this weekend now
Cheers
Rod

[williams4x4]

Rod, if it is that the viscus is gone give me a PM I have a spare you can have, just cover the freight

[Bikedude]

Thanks williams 4x4.
, I will check out the fan
Rod

[williams4x4]

No worries mate, just happy to help where we can

[frontier1999]

Hell!! thanks for all the info - i was worried about the sensor and the use for it. mine is manual and that means i can just tie the wires up!

[isuzumudman]

So, what was the solution and conclusion??

[williams4x4]

I sent the (OP) a replacement viscus unit "for free too" must have been a good day for me lol, think its sorted the problem from what he said in his last email