My 87 4Runner had the most finicky gauge I have ever seen. Most of the time when you key on the thing moves to the center and stays there. Sometimes (rarely) it actually works and stays on C, then rises as the truck gets warmer like its supposed to. I don't think its the sender, it sounds like a loose wire or bad ground. Anyone got some suggestions? Its a 22RE with analog factory gauges.

 

I think that it could be the sender. I am not sure how they work, but if there is any coiled wire in there with a short, there would be enough resistance to cause it to only go half way. If there was a short in the main wire it would probably either go all the way or do nothing at all. There is also the chance that it could be the guage, but I would check the sender first.

 

If the sender is located on the top of the engine, on the intake (or head I don't remember, but you can access it easily from the top of the motor), roughly halfway back on the motor then I've replaced it. That was the only sender I could find that looked like the gauge sending unit. I'm pretty sure that was the correct sending unit. Could anyone out there let me know if that's right. If that wasn't the right sending unit, where is the right one? And if that was the right sending unit, any more suggestions as to what may be causing the problem?

 

where exactly is the sender for the temp gauge? its a 22re.

 

I had a problem just like that on an old Nissan Maxima. I tried everything, and it ended up being the guage itself(the one in the dash). That's where I would put my money.
Ironically my friends 88 4runner does the same thing as yours and my old nissan did, and he refuses to believe me. He also has checked the sending unit. I really think that he is just lazy, and doesn't want to dismantle the dash.

 

A temp gauge is usually easy enough to check. (I don't have a manual here so this is generic...) Find the sending unit and unplug the wire from it. Turn the key on and the gauge should be all the way one way. Touch the sender wire to ground and the gauge needle should go all the way the other way. If not, it's a bad gauge. If it does, it's either the sender or the ground for the sender. Remove the sender and clean the threads and reinstall it. Check that the ground strap for the engine block isn't loose or corroded. That's about all there is to it. Also, come to think about it, have you been doing any wiring modifications in your dash? Stereo install, accessories, etc? I occasionally see where someone installed a high powered stereo or a bunch of other accessories and hook the power and ground to the dash wiring. Can end up with not enough ground path for the current, and resistance gauges like temp and fuel can read wrong. Just a thought.

 

Temp sender is behind the thermostat, down low on the intake manifold.