Help? 2002 - 2.7L with 250,000+ Temp gauge jumps

I have flushed the system changed the sensor and thermostat with no change to the needle jumping up and down to normal. I just recharged the Air conditioner 2 weeks earlier when the faux pas started?

 

There are actually two sensors on the 2.7L. The singe prong version is on the coolant outlet (passenger side cylinder head). The other is on the back of the cylinder head and has 2 prongs. I believe that sensor is what controls the temp gauge. I will tell you I have added an aftermarket gauge as my stock gauge is worthless.

 

thanks but I cant find the 2 prong? the dealer shows only 1 for the coolant and a sensor for the oil witch is on the lower block? could that be the 2 prong ?

 

It is on the very back of the cylinder head, against the firewall.

 

do I have to lift the motor? I can see just the hose clamp under the black plastic cover or do I have to remove the wire harness to access it? not user friendly?

 

It is not easy to get to. You MAY be able to reach it from the underside, but I would disconnect the 3 connections to the ECU (behind the glove box), pull the harness through the firewall and lay it over the intake manifold. It will allow a better view. You will have to get to it from the passenger side. It will be easiest to remove the hood also.

 

wow ! to much labor to hire out , since Toyota replaced the frame at 175,000 I take the ole girl off the road in august and pull the bed and do my annual grinding to the body and rear end due to northeast salt! I always replace the fluids in the drive units and toy with the parking brake! thanks for the details I wouldn't known to unplug the ecu from the inside! let you know how I make out in aug. thanks again spud

 

The sensor with 2 wire connector is used by the engine computer. The computer has its own ground.

The single wire sensor is what the cluster gauge uses. it's just grounded to body ground.

I'd think it's unlikely that this sensor would fail in this way to cause these symptoms (fluctuations), but it could be a bad connection somewhere. Or it could actually be a problem with the cooling system.

You could hook a scan gauge up to the OBD port and read the coolant temperature from there in real time as the engine is running and compare to the cluster gauge. Each uses a different sensor, so if they match then it's unlikely a problem with the sensor itself.

 

Gauge ground could be an issue as well. I went aftermarket and I'm running a scangauge at the same time. Consistent Temps on scangauge and aftermarket, but my stock gauge is all over the place. Before the rebuild, it was consistently at the half way mark once warmed up.