pascoscout

1988 4runner 3.0V6, Auto Trans, SR5

Been having trouble with my temp gauge. It started when I tried the "Definitive Temp Gauge Fix". My gauge seemed to jump right to the middle and stay there. For what its worth I found no broken wires on my original gauge but when I put it back in it no longer reads correctly. I've since replaced the gauge with a spare I had and replaced the sending unit. No change.

What it does: When the truck is cold (and I mean 20 degrees over night cold) the gauge sits at the bottom like I think it should (first pic). When I turn the key to on (not started) the gauge jumps up about 1/3 the way(second pic). I start the truck and drive it and in a few minutes, or about a mile of driving, the gauge is up to the bottom of the red line (third pic). It hardly moves from there even after hours of driving though I did see it creep up a little bit on a long hill climb, dopped back down to this spot after a few minutes of idle. When I turn the engine off (power still on) it drops down to about 1/3 the way. Power off and key out of the ignition it goes to the bottom again.

I've checked with my temp gun and I am running around 190 when the gauge is maxed out which seems to be ok, not overheating.

Seems to me that if it wasn't jumping up to 1/3 the way with the power up it would be right around the middle once the truck reach normal operating temp (where its pegged now).

Can this gauge be adjusted so it reads right? I didn't notice that there was more than one way to put the pointer back on when I reassembled the gauge the first time or when I replaced it. Seemed like you'd want it pointed at the bottom with the power off.

Any thoughts or ideas?

Terrys87

iTrader: (1)

I have seen the sending unit have a green crust build up on it and that cause a gauge to jump all over the place. Try taking it out and give it a good cleaning with a brass tooth brush. Also there is a ground wire by the fuse box inside the drivers side kick panel. I take the ground wire off and make sure there isn't any corrosion on the terminal and the body.

Also if your runner has the rear heater option I believe here is the correct Thermostat that can help cut down some problems.
Part # 90916-03070 for Dual Stage Themostat

The pictures below apply to a 22re but I feel most everything would apply to the 3.0 as well.

Here is a picture of a dirty Temperture Sensor. I have seen worse. I chipped some of the scale build up off so you could see a difference.


The sensor sits just below the Cold Start Injector in the Intake manifold. Uses a 17mm deep well socket and is a 5 minute job.

Gamefreakgc

The engine coolant temperature sender circuit is very easy. Power is supplied, goes through the sensor, then to the dash gauge. That's it. 99% sure it's an issue with the sensor, try the above method or buy a new one.

RJR

The jump to 1/3 scale when cold before starting the engine is instructive. Given the simplicity of the circuit, that can only happen (assuming the gage and sensor are good, and you've replaced both of those) if you have a parallel leakage path to ground in the sensor lead. Check the leads btween the gage and sensor carefully for corrosion and lack of insulation integrity. Also, pull the connector off the sensor and see what the gage reads. If it reads anything but "cold" you pretty much know you've got some bad wiring.

The other possibility is that you have a mismatched gage/sensor pair. If the gage is expecting a certain resistance curve from the sensor, but the sensor has a lower resistance curve, you'll get the behavior you describe.

pascoscout

I'll check out more of the wiring in the circut. I bought a new sender fom napa and put it in a week ago (before I posted this), made no difference. Maybe I need to get one from toyota but seems like that wouldn't be it as the original one in the truck worked at first and then started doing the same thing.