Yamaha TRX850 Enthusiasts Forum

Hi guys, Don't know if all TRX's worldwide were the same but the thermatic cooling fans on Aussie spec bikes only turn on when the coolant temp gets to just over 100deg. (UK owners would probably never have experienced this ) This can be a bit worrying, sitting in peakhour traffic in summer watching the needle on the gauge creeping up & up & up ..........
Does anyone know if there is a different sender unit available (either genuine Yamaha or aftermarket) which will turn the fan on at a lower temperature - about 90deg maybe?

Very likely yes, you would need to ascertain the thread diameter and pitch and then search online for one with a lower operating temperature.
You could also try mixing up a stronger ethylene glycol and deionised water mix for your coolant, the bike will run cooler with a higher ratio of EG to water. Yamaha specify a 50/50 mix, I tend to go a tad over that, maybe 55/45.
Obviously this little trick will make your fan even less likely to cut in.

I remember with my first car we installed a Davis Craig Thero Fan and that had a switch unit that woul allow me to raise r lower the temperature that the fan would cut in at. Could it be as simple as getting a switch along these lines and fine-tuning it for yourself???

Yep it could be, check out Kenlowe fans site:

http://www.kenlowe.com/fans/consumers/fans05.html

Scroll down to Adjustable Automatic Temperature Conrol and you can view the diagram and rheostat to adjust the temperature at which the fan will come on.
Alternatively you could rely on your own diligance to flick a small switch on when you get concerned about the temperature. Basically take the single wire that fixes to the temperature sensor by the thermostat housing, route it to one side of an on / off switch and take the other side of the switch to earth / ground.
That small switch will then make the earth just like the temperature sensor would.

Thanks for the info guys - will look at the adjustable rheostat thing at my local auto shop too. One question Mincehead, if I do as you suggested & run another wire to a little switch somewhere for manual operation, will the fan still work "thermatically" as Mr Yamaha intended if
I leave the original wire in place too? ie: if I splice into the wiring plug at the sender unit.

YES, it should. I was going to suggest that option too. I believe the original themo sender simply creates an earth return, the fan will likely have an igntion derived live feed to it and relies on the sender to complete the circuit.
Although if you leave the switch in the ON position you`ll be creating a continual earth so you must flick it off to allow the circuit to work as Yamaha intended.
Try it, it won`t take long to do, you won`t even have to mount the switch just leave it loose while you go for a ride to check it out / get the bike up to temperature.