Hamwich, look in "car builder solutions" on line and replace the whole in-line sensor housing and sensor as a starting point. The thermostat opened at 100'c you said.... mmmm, that is probably a little high! You will need to check but I have a feeling that it should be a thermostat that opens at either 85' or 90' c. that could explain you raised head temp on measuring. Is your engine still a CVH Ford and is it injection or carb fed. I'm sure there is a difference in thermostat opening temp however if you cant find the info out whip the stat out and it should have a temp setting on it, as it was working fine before a replacement should be ok. When the stat is out check it in a pan of water with a thermometer and see the true opening temp.
That's a quick answer but i'll read your tale more slowly later and try and get some better logic into it!
It's a 2007 Vauxhall Ecotec Z18XER 1.8 VVTi engine, Sewin, as fitted to the Astra and Zamora SRi at that time. The ECU is a MBE unit with custom map by John Ravenscroft of TVR. The operating temp range of the head is 120C, the ECU is set to switch the fan on at 100C but you're right, I would expect the thermostat to open a bit earlier. Maybe it's that that's knackered.
EDIT:Just checked and the thermostat on these engines is set to open at 105C, which I found surprising.
The feed to the dash gauge is from a traditional sender plumbed into the radiator return, so I could keep the original Smith's dash gauge. I've already ordered a replacement as they are easily obtainable, I'll see if I can find a replacement thermostat from somewhere.
