Temp Gauge erratic? Tried fixing....not fixed

2001 Tacoma v6. Temp gauge reads cold for way too long, then erratically moves between normal and cold, bouncing. I replaced both temp sensors (one in the front and one in the back). STILL NO READING...any suggestions?

I haven't driven it yet, but it currently isn't reading again after getting warm. Not sure if it will even bounce erratically anymore.

I have read as many forums as I can find, so if you know of one and want me to read it, let me know please.

 

Ok, so I drove the truck (it is about zero degrees out if that changes the trucks attitude I don't know). The temp gauge didn't read for quite a while, then, after about 10 minutes of warming up and 10 minutes of driving it finally read at normal operating temperature. It wasn't bouncy or eratic. But it was warm before it ever read, so I am not sure why it still isn't reading at first, even after the engine is warm (and blowing warm air)?

The one thing I haven't changed is the thermostat? From everything I read it should have been the sensors.
Any thoughts on the thermostat?

 

It's possible for the temperature gauge itself to go bad.

However ... Since the problem seems to go away as things warm up, I suspect it's a wiring connection that's loose / open when cold and then gains contact as things heat up.

Just for the record ... The water temp sender / sensor is the only sensor that has anything to do with the temperature gauge's functioning. The engine coolant temp sensor (rear one) is what the ECM uses to 'read' engine temperature. This doesn't involve your cluster temp gauge at all.

The original behavior you described (with the gauge 'bouncing') sounded more like a gauge or gauge circuit problem. The later behavior (delayed reading with no bouncing) might indeed indicate a sticky thermostat.

I'd recommend checking the thermostat - if nothing else, to rule it out and confirm it's a gauge circuit problem.

 

I think you are right, narrowing down the problem of the erratic gauge to wiring. Now that it reads sometimes when hot, but not all the time, I am going to try finding the ground, and troubleshooting the wiring.

Not sure where to start (if anyone has any suggestions that would be great).

I still haven't replaced the thermostat, but I don't think that is directly related.

 

Thanks for the help. I started the truck when it was slightly warm (I think). The gauge was reading about 1/4 the way up for the first time in a long time. When I shut my door, the gauge stopped reading (ground I am thinking). I opened and shut my door again and it started reading at about 1/4 the way on the temp gauge.
So, I pulled the plastic off the floor and uncovered the ground, which I have messed with for the grey wire mod. I disconnected the ground and there were no issues with the temp gauge, worked just fine? That confuses me.

So, I tightened the grounds up anyway and am hoping for the best.
It was reading hot when it got hot most of the time now. But one time it read a 1/4 when it should have been reading hot, and I am curious if that has to do with the wiring also?
Any help is appreciated.
Thanks.

 

You're definitely on the right track - it's a wiring issue, probably involving a bad connection, short, or bad ground.

Your grey wire mod affected the ABS and Rear Diff Lock warning indicators in your cluster. These are on the same internal circuit as the water temp gauge. The water temp gauge is the component at the 'end' of that circuit, the point from which the ground line goes out.

I'd suggest undoing your grey wire mod to see if the water temp gauge problems go away (just as a check). If the temp gauge starts working correctly, I'd then go back and re-do the grey wire mod to eliminate whatever wiring fault there is.

It might be as simple as a short around the 4WD ECU.

 

Thanks for explaining the gray wire mod stuff. So...on the gray wire mod, I added extra wire so it was easier to work with now and in the future. Can the extra wire be causing the problems?

 

Mine has been doing this recently. The bouncy needle, and lately it doesn't even bounce, just stays on C. I think I'm just going to install an aftermarket gauge/sensor.