Transit mk6 (2000) 2.4l diesel temperature gauge questions

[Pres]

Hi, first time poster 'ere

My dashboard temperature gauge is doing some funny things on me.
One week it will be sitting at just under half consistently.
Then after a little while, i will drive and it will sit at a bit over half rising and falling slightly but never going past 70% . This continues for around another week. Give or take.
Then it will go back to sitting at just under half for the same (1 week)
This cycle seems to continue...

I've had the thermostat replaced, fuel filter and it filter. ( If that means anything)

Could this be a computer issue, or is the dashboard gauge not reflecting the actual engine temp?
Any info would be nice. Thanks

[wojciech]

Propably CHT sensor is broken. It is semiconducor (resistor NTC) and it works in two ranges: first from -40 to +78°C, and second from +62 -to +214°C.
Typical CHT sensor failure is that it works correctly in first range, but in second reading is erroneous - because work terms of semiconductor structure are to strong (temperature and higher voltage).
For example CHT sensor output voltage B=+2,5V it can means C=+35°C or +129°C (look for the picture). If "pull up" resistor (no.2 on the picture) is on - PCM (analog/digital processor no.6 and 7 on picture) read it as +124°C, if resistor is off - PCM read it as +35°C.
In your case problem is with correct voltage in second range.

Change CHT sensor using special 15mm socket (high for min. 80 mm, with 4 mm slit for electric wire). Use white ceramic paste for it.

[Pres]

Wow thanks for the comprehensive reply. Will do this asap