As it turns out my apparent overheating problem looks like the gauge is telling porkies.
I checked it with a temperature gauge/probe and it looks like the engine is about 20deg cooler than the car’s gauge suggests.
Is this purely the gauge at fault or could it be something else?
Cheers
Robbie
Surely your best option is to fit a new gauge?
No reason to suspect that if the gauge was faulty there is any other problem with the car’s cooling system, but I assume you wont feel comfortable driving round with a gauge you can’t rely on. If the temperature stays within normal operating limits once a new instrument is fitted, then you can rest easy.
You have three options:-
The gauge
The sender
The voltage stabiliser
John 
Yeah, I thought about the Voltage Stabiliser, am I correct in thinking that it’s part of the alternator and the only fix would be a whole new unit?
The voltage stabilizer is a nasty little electrico mechanical thingy at the back of the dash. It provides 10 volts for the fuel and temperature gauges. There are now much better, cheap (less than a tenner), solid state electronic ones. Suggest you get one - look at ebay, and specify positive or negative earth. Fit this before even looking at the gauge or sensor.
best regards, iain
Robbie
John.p.clegg retails these uprated (solid state) voltage stabilisers built into original cases for negative earth fitment only at about ?10:00 plus P+P,guaranteed accurate to 0.1v…
Drop me a line if you’re interested
John 
P.S.
Is that me? 
Any photo`s of the voltage stabilizer so I will know what to look for
Try again,something like this…
John 
Hmm,. After Iain’s post I checked my manual and it said that the Voltage Stabiliser for the charging circuit is now built into the back of the Alternator (17ACR).
So is there another one for the gauges behind the dash then?
Robbie,
You are getting a little mixed up here, the charging circuit has a regulator to control the output of the alternator and the gauges have a stabilizer to feed them with a constant voltage to “stabilize them”
John is that a stelf bomber I dont see!
Robbie.
The thing your looking for is this:
holden.co.uk/picDisplay2.asp … 70_118.jpg
it is behind the speedo or tach. It just does the instruments not the charging.
best regards, iain
Ah, I see, thanks Brian.
If this stabiliser was playing up, would anything else be showing symptons aswell?
The fuel gauge works ok, oil pressure is steady but only reads 32psi, voltmeter never seems to go into the on charge side I but never have any charging problems either, oh and the clock doesn’t work but I think thats something else.
edit: Thanks Iain for the pic, seems we posted at the same time 
As far as I know the stabilizer only controls the temp and fuel gauge.
Brian
Never did get the hand of this electrickery thing…
John 
Robbie
Yes,the fuel and oil gauges will also be reading wrong,but with them all being dampened it’s difficult to notice the readings change with engine revs (voltage fluctuations)
John 
Ok, thanks John.
I’ll let you know about the stabiliser 
Robbie,
I had exactly the same symptoms. The temperature read high. With a solid-state stabilizer it reads accurately now. Actually the fuel gauge tends to look low, but that reflects the difficulty of filling the tank right to the top.
best regards, Iain
Thanks again Iain, although the wiring diagram confuses me! They all do actually 
Another thought; is it possible to get at the voltage stabiliser without removing the dash?
I cant say for sure as I’ve never done it on a plus 2 but I’m sure it is, I’ve done it on the small Elan and Europa, even if you have to take out the rev counter/speedo to get better access, but dont forget to DISCONNECT THE BATTERY FIRST and take note where the wires go to…make a drawing
Just a thought, you dont have to take it out if you are replacing it, just take off the wires and fit them to the new stabilizer then find a convient place to mount it.