Temperature gauge issues

Hello everyone, I have a 2012 Tacoma 4.0 off road. Been a fantastic truck, yesterday when I would drive the truck and get it up to operating temp and stop and put it in park or neutral the temp gauge would drop straight to cold and engine would idle high as if the truck was just started first thing in the morning (I live in NC it’s definitely not cold outside right now). I put a new thermostat along with a coolent temp sensor with no change. Can’t find anything on this matter, if anyone has any input it would be appreciated!

 

I’ve seen this with thermostats but clearly you changed it.

is the cooling fan loud? The clutch make be sticking.

 

To me it sounds normal, I may have to do some more investigating on the fan. What is strange is when I put it in park/neutral and then gauge goes to cold as soon as I put it drive it rises slowly back to operating temp.

 

Bishop84 what’s the best way to test out the fan to see if that is a possible candidate to the problem.

 

Used to go the kamikaze route, hold it when starting and see if you can hold it. If you can, its good.

The proper way is to know what its supposed to feel like at a stop, vs bad at a stop. It's a trained thing. But it should spin freely when cold.

 

Gotta say, this sounds electrical to me. Your sense regarding the coolant temp sensor was, I think, a good place to start. I saw a diagnostic done on South Main Auto where a bad temperature indication to the ECM caused a very rich condition.

What I can’t figure out is how the gear selection could have anything to do with that temperature reading. It would be interesting to look at a couple of wiring diagrams to see if there is any connector where the transmission wires and the coolant temp sensor both go through. Seems unlikely, but would be good to know, as that would be the first place I would look.

 

The cluster has those wires (if it’s an automatic).

 

The problem is you are low on coolant. When the engine is running and loaded the coolant is circulating and wetting the temperature sensor giving a reading. When you place it in park or neutral the coolant flow is decreased and the temperature probe is not in the liquid causing a cold reading as it is a wet bulb probe and needs to be in the liquid to read the temperature.

Top off the coolant.

 

I'd suspect a wiring issue, is the CEL on? If so what code(s) is it setting?

 

Dm93 it is showing code P0125

 

Can you scan tool show coolant temp?
If so see if it's within about 10 degrees of ambient temp when the truck has been sitting overnight.