+1 for not having enough water in the system.  You need to run the car with the cap off and then fill the radiator when the thermostat opens and the fluid drains into block.

I tried bypassing the heater from the inlet manifold to the water pump but made no difference. I converted from 1.6 to the pinto so am unsure of how it ran previously but i did have the block and head hot tanked and tested and all was fine. No bubbles or exhaust smell and its a brand new ally 3 core radiator. i bought a new thermostat today and notced that it was different to my old one. The old opened at 191°f and the new one opens at 188°f as per the tridon book at supercheap. Ignition timing is bang on 6° but i might re check the cam timing but the markers all seem to line up.

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.

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

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

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.