RS 2000
At this point You really need to confirm the actual temperature, you may have faulty gauge/sender.
Cheers

Gdub
You need to put a temperature probe into the water to determine if the guage is actually reading right.  I have seen many people waste a heap of time and money replacing parts because the gauge was reading high when the engine was operating normally.  Eliminate that possibility before going any further

 
First thing I would do is listen to people with experience & keep it simple. Have you checked that the gauge is actually reading right? I have seen a lot of cars (particularly Escorts) that have problems with gauges.

Took the sender out and put it in some boiling water with a thermometer and 100°c is about just below the red on the guage. I ended up making the carb run rich and advanced the timing to about 8° and its sit on or just about half at idle so i am hoping this might have been the problem.

Gauge shouldn't read red at 100c, it is wrong. your gauge is showing more than actual. I have posted gauge and sender specs somewhere on the forum so you can diagnose if it's sender or gauge that's at fault. I can repost the specs tonight when I am at my pc.

Cheers

For now why not run the thermometer in the filler neck at idle and get the exact idle temperature so you can compare that temp with whats showing on gauge.


Cheers

Its sitting just below red the sender i have has 120°c stamped on it so pressume thats the max temp it will go so would i be right in saying that 100°c would be around the 3/4 ish mark?

Thanks for all the quick responses

To check your gauge you need to disconnect the sender and connect appropriate resistor(I use variable resistor) between the wire and engine block/head(ground). Gauge specs are C=73ohm, N=25ohm, H=10ohm
The sender is the same on the non RS Escorts.

On the gauge in my Rs and the spare dash I have 25 ohm brings the gauge to the second white line which is around 2/3 of normal range( area between blue and red). From my testing this happens to be around 100-105 Celsius.
 
I don't have a non RS dash at the moment to test, but I would suspect that it would behave the same considering it uses the same sender. hopefully this  info helps your diagnosis

Cheers
 
For reference here is a pic of RS temp gauge

Is this how you would test a temp gauge using a variable resistor? Wire the resistor between a negative and the existing wire connected to the temp sensor. Using a volt meter, measure how much voltage the temp gauge is receiving after the resistor. Adjust the resistor for different readings on the temp gauge. In relation to where the gauge is sitting match the gauge to what voltage it is receiving to what voltage it should be receiving. If it is receiving the voltage is should be relating to where it is sitting its accurate. Lower the voltage the gauge receives the higher the temp reading and vise versa.

I hope I have worded everything well enough to understand. I'm going to give this a go on my Escort. Would All MK1 and MK2 Escort temp gauges work off the same voltage? Might be evident that electronics isn't my strong point.
 

hey eskie92,
Forget voltage for this test. you don't need volt meter, you only need ohm(resistance) meter.
Use your ohm meter to adjust your variable resistor to above specified resistance then place the resistor in place of the temp sender and after turning ignition on your gauge should show relevant temp. Your little diagram is ok, it doesn't need to be battery -ve it can be any good earth such as engine block, after all that's how temp sender earths.
So if you apply 73 ohm resistance the gauge should show cold (blue section on RS gauge), if you apply 25 ohm it will show 2/3 of normal range(second white line on RS gauge), and if you apply 10 ohm it should show red on the gauge. Like I said earlier from my testing 25 ohm or 2/3 on the gauge corresponds to around 100-105 degrees Celsius.
 
 
cheers