Yes, I'm back with yet another problem for you great people to solve,

Here's the issue;
I can drive around at 80km/h all day without any problems. But, as soon as I creep the speed up to 100km/h, my temperature rises up so bloody quickly it's at the Hot mark within about 10 seconds. Back off back down to 80, and by the time you're at 80, the temp is back down to normal!!
So, seeked a few peoples opinions and tried to do some trial and error. It came down to 2 things. First thing which I tried was to take the radiator out entirely, and flush it and clean out any rubbish which has found it's way into the radiator. Didn't hold much hope that it'd solve the problem but thought it can't hurt anyway..... And as expected, it didn't solve the problem.
Next thing I tried was to change the thermostat. Seemed more logical given the temperature sender is right above the thermostat, so thought it'd be the problem for sure. Found me a nice new thermostat (did someone say Daihatsu Rocky? Ahh yes, you did, hold on one second while we just triple the price for you!), took the old one out, nice new gasket on it, and all back together. Topped the coolant back up and off we went for a test drive.
Well, I don't quite know if 'interesting' would quite fit the results of the new thermostat,

Just out of curiosity, I sat there stopped, and took the rev's up to where they'd be at 100km/h. Think it was there for about 5mins, and the temp guage did not move one bit. It stayed on a perfectly normal temperature.
The drive back to Isa, the temp was about normal nearly all the way back, even with the air con on. Think a couple of times it did warm up slightly, but wasn't long before it went back to normal.
So now it's got me bamboozled. I can only think of 2 more issues it could possibly be. 1 is the temperature sender or the guage itself. The 2nd one, and I consider it the absolute last thing, is the clutch thingy in the cooling fan. The fan appears to be operating normally though.
SO, ANYONE HAVE ANY IDEA WHAT MY PROBLEM IS!!!! Pleasssssse!

Cheers in advance.
Floody