1kz temp issue

[Boost_4_Life]

OK, I have houded all the Hiace forums so now toyspeed its your turn...

bought another supercustom, 1998 model in good cond. 1kz-te diesel.

Strange thing happening, in that it doesnt run up to proper temperature most of the time. Instead of the gauge sitting on half, it sits sometimes between half and quarter... First thought was sticky thermostat, so changed that. Prob stayed the same. When we flushed the coolant to do thermostat it was all clean, and radiator is in good nick. When thrashing up hills, the temp may finally get to halfway, then on the flat it will drop again.
Sometimes however, it will decide to run up to temp for a couple of weeks, and every time you drive it it will be fine, running on half. Then it'll randomly decide no i'm gonna run cold again...

The gauge does not jump or skip, and i've checked all connections so I dont think its an earthing or connection issue. I even pulled the dash apart to see if the gauge had had the common resistor mod done to make it more sensitive... nope its stock.

It's not using any water and doesn't ever go over half, cooling system seems all in good nick which is critical for these beasts. I dont think its a stuck viscous fan, but how could i tell? I'm not overly worried, just wanna know what the hell it could be... dodgy sender maybe??

any pearls of wisdom?

[rollaholic]

if the fan is running locked up full time it will howl like a mofo. not to mention you wouldnt be able to spin it with the engine stopped.

what thermostat did ya put in it?

[Boost_4_Life]

just the standard spec tgp replacement

[CAMB01]

+1 for fan staying locked up.

[Mr Revhead]

As above fan is easy to tell. Give it a spin. If its not that then temp sender is next.logical thing.

[Boost_4_Life]

well never hear the fan roaring as such, just freewheeling so maybe ill try another sender. Mark to the rescue (again)!

[DFECTED]

when it runs cooler, is the a/c on?