My gauges just don't go further than 80, still need to measure with MES but they also seem to be very inaccurate. And read quite some similar stories. But can understand it's a bit worrying when you see that needle at that place...

Some measure it like this (clearly not having the cap on while it warms up to avoid that hot coolant bursts because there is pressure on it).

 

You could have a faulty gauge, it does happen, just remember the cars no "spring chicken".

However depending on which model your car is it may be the Temperature sensor. Earlier CF1 cars just had a two pin sensor, both ECU and gauge read the same data, as the years progressed we went to a 3 pin (CF2) then 4 pin (CF3/4) sensor, which took separate readings for gauge and ECU.

So you might want to try changing the Temperature Sensor first, much easier to do.

 

Does your car have a/c? If so the rad fan will run when it's on, regardless of engine temp.

Possibly your car will have 2 coolant temp sensors. One signaling the engine ecu for mixture control, and one for the gauge.

 

Pepenacho - Just re-read your original post and realised that yours is a PH1 car so only uses a 2 pin sensor, I would still replace it to remove it from the equation. Then check wiring to gauge and ECU for integrity.

When driving does MES show the car reaching normal operating temperature?

Possibly your car will have 2 coolant temp sensors. One signaling the engine ecu for mixture control, and one for the gauge.

Just done a little research and apparently the Ph1 GTV actually does have two temperature sensors fitted, there is one for the Thermostat and one fitted to the radiator for the Radiator fans. Without looking into the wiring diagrams I can't comment if it has any effect on the ECU or gauge readings. As far as I know both still take their info from the sensor mounted to the thermostat.

Alfa Romeo GTV/Spider Temperature Sensor – CF1

 

Yep, generally on these earlier cars the ecu doesn't control the temp gauge or the rad fans, so there may even be 3 separate signals. The one in the thermostat can actually be 2 separate sensors, with one signal for the ecu and one to the gauge. The one in the rad will just be a temperature triggered switch to turn on the radiator fan. These things get more complicated with a/c, hence why I asked.

Pepenacho needs to look at their engine bay and determine what exactly they have.

 

Ok, after looking at the service manual and wiring diagrams have sussed out the intricacies of the early Ph1 cooling sensors, and sprint_veloce is pretty spot on.

#1/ On the Thermostat there is the Coolant Temperature Sensor (2 pin)
#2/ Next to the Thermostat and plugged into the engine is the Coolant Temperature Gauge Transmitter and Max. Temperature Warning Light Contact

So first thing I would do is remove both plugs and give them a good clean with contact cleaner and see if there is any difference.

Also check using MES and see if the car reaching normal operating temperature while driving.

 

Thank you for your answers. That's right, my car has got two sensors at the thermostat housing and a third one in the radiator, the problem is that all of them are new and I've already tried cleaning their connectors with contact cleaner. There is something which I have noticed: some of the wires look a bit toasted (sensor 2 of the diagram). I'll try to jump them to see if it makes any difference.
Apart from this, it doesn't make much sense to me having one sensor in the thermostat for the ECU, a different one at the radiator to control the fan and another to control the interior gage. Which are the benefits for such a configuration?

 

Thank you for your answers. That's right, my car has got two sensors at the thermostat housing and a third one in the radiator, the problem is that all of them are new and I've already tried cleaning their connectors with contact cleaner. There is something which I have noticed: some of the wires look a bit toasted (sensor 2 of the diagram). I'll try to jump them to see if it makes any difference.
Apart from this, it doesn't make much sense to me having one sensor in the thermostat for the ECU, a different one at the radiator to control the fan and another to control the interior gage. Which are the benefits for such a configuration?

There are no benefits, the engine ecu's Alfa used in the 90's simply did not have the capability to control the cooling fans or temperature gauge. So these were separate systems.

This functionality was quickly added to the control units such that my 2003 156 has just one temp sensor in the thermostat and the engine ecu controls the dash gauge and radiator fan.

 

Well your supposition would explain why in later cars they switched to a single Temperature sensor mounted in the thermostat with multiple pins, as I described earlier.

 

Don't forget, when you have a chance, take the car for a drive while hooked up to MES and see if the Coolant Temperature gets up to operating temperature.

 

Today I went for a drive to check the temperature with MES connected. It didn't pass 67º C while the gage in the dash was way up the 90º mark closer to the next one. It is at 67º when the radiator fan starts so I think each of the three sensors reads a different temp. Which one to belive? I wish the one in the radiator is correct to avoid burn the headgasket. The problem with the ECU sensor is that it will foul the ECU to do the right air/fuel ratio. I think I have around the old sensor, I'll put it back to the car and see if it makes any difference. Thank you all for your responses.

 

No, I can't find the old sensor. Does anybody know the OEM reference and brand of the sensor? I'll buy a new one and I'd like to make sure is the right one. Thank you all for your responses.

 

I've found this but not sure if this is the right one. https://m.autodoc.es/bosch/7005118

 

It looks like the correct one, to be sure though you can find the correct on here, top two items in the list are for your car - GTV/Spider Coolant Temp Sensor