my 1300 felly used to run at about 80,than all of a sudden ran at 90 bang on the half way on the guage,now its creeping up all the time and have to have the heater on to keep temp at 90 as soon as the heater is switched off the temp shoots up to 100+ fan doesnt kick in, changed temp sensor thinking that would sort it.it aint,any ideas,valve clearances,radiator seems ok,thermostat fan sensor switch or what? please help.

Anyone else think "thermostat"?

The fan should kick in somewhere between 94 and 99 degrees, so either the fan switch has gone, or (more likely) as Ken says the thermostat or its retaining clip has failed so it's not opening properly.

i thought it was more like 104-105 C before fan kicks in?

i thought it was more like 104-105 C before fan kicks in?

On the gauge, yes - that spec is for the switch itself, and a 5-10 degree difference in coolant temperature between the head and the radiator isn't unreasonable. Remember the fan switch is completely independent of the temperature sensor