Ever since i got my 86 runner, Ive noticed that the coolant temp gauge in the cluster does nothing. it almost always jumps to a little under halfway as soon as the truck starts. Sometimes it wont move for a couple minutes and then jump to its usual position. The trucks overheated a few times since ive had it due to my stupidity, and it still says a little under halfway as the coolant is boiling over inside.

is this a faulty sensor? or is it a more involved electrical problem?

 

Yes. Er, No. Well, maybe.

If you're willing to accept uninformed guesses, there you go.

Personally, I'd look at the manual and use that to diagnose the problem.
http://www.ncttora.com/fsm/1990-1995...e/combinat.pdf

 

Unless you are starting it just after shutting if off, the needle should be at zero and work it's way up to regular operating temperature. Mine usually takes around 4-5 minutes to get there.

 

do you have the cluster with the tach? i had the standard which worked fine then when i switched to the sr5 cluter the temp gauge doesnt work and the oil pressure either. my temp gauge does whgat your saying almost exactly. possibly bad cluster?

 

It's pretty cheap and easy to just replace the temp sensor, maybe 10$? I'd do that right off the bat and then you can mess around with the FSM testing procedures.

 

I had the exact same issue when I swapped in a motor from a non SR5 truck to a truck with SR5. Also, my oil pressure gauge doesn't work. I'm guessing these 2 sensors are SR5 gauge specific.

 

Sounds like the behavior of a faulty switch....if you have overheated the truck, it is likely you need a new one. $15 at most autoparts stores and takes 5 minutes to replace. Wait for your truck to be cool and just unscrew the old one and screw the new one in. You won't loose hardly any coolant if you keep the cap on your radiator.