Water problems 300tdi in a 1985 110

Hi
I spent last night reading through the many posts on this.
Overheated out of the blue on a short run so i started by changing the sensor, then the thermostat ,then i replaced the radiator, then the water pump, i changed all the water pipes for new, i tried all of the various methods of bleeding air from system at least 4 times
It has no oil in water or water in oil, i get no bubbles in the header, i have good exhaust fumes, it sounds lovely! Heater blows hot air into cabin no problem, it loses no water.
Gauge gets up to hot slowly but gets all the way up and it does appear to be hot in the header tank but not boiling...the radiator doesn't get that hot but is warm and all pipes are warm...it feels to me that its not circulating properly but i cant keep flushing it (done 3 times) and not sure what else to change.
I can think of nothing else but gauge is wrong or head gasket (i have never had all of the above with a failed head gasket).
Anybody any ideas i have missed..i think i will change temp sensor again and finally the head gasket but was hoping some one would know better!
Any Advice gratefully received as ever
Matt

Doesn't sound 'hot' to me ....

Why do you think it's overheating ?
There are two types of sensors/gauges, you need to match the pair.
The key is the colour band on the sensor, is yours green or black ?

'Normal' is around 90 degrees C, you can test this by filling a cup with boiling water and dangling the sensor in it. The green wire (from the gauge) has 12V on it and the body is ground. the ground wire can go in the hot water but not the power/green wire.
If the gauge goes up to the Red, it's the wrong combination.

I've just changed mone for a Stack, if you want a working pair I can send you my old set for £60.