Yamaha TRX850 Enthusiasts Forum

Hi , need some advice on what temperature the temp gauge will show on an open road.

Mine shows about 65 , which I think is low.

I have idled the bike for a while , watch the temp gauge go to about 105 - 110
and the fan kicks in , temp drops to 95 or so , fan switches off. I have tested
the thermostat , opens at approx 85 and fully open at 95.
I have stripped the thermostat housing , still in pristine condition
I could not see any bypass of the thermostat either ,

So all looks fine but under normal riding conditions the temp does not go above 65 ....

I am wondering what other TRX's average temperature is on the gauge , maybe I am trying to
fix something not broken ?.

I am wondering what other TRX's average temperature is on the gauge , maybe I am trying to
fix something not broken ?.

Yep thats normal.

Hello and welcome.
The TRX is not a hot running bike. It takes a lot of slow traffic and hot weatherfor the fan to kick in.
Normally they don't run much over 60 or 70 in normal open road conditions.
If you've checked that the fan does kick in if ever you needed it, then I dont think you've got a problem!

Everything is working perfectly and 65 degrees is the normal working temperature.

Smithers wrote:Everything is working perfectly and 65 degrees is the normal working temperature.

Perhaps the TRX radiator is a bit too big? A petrol engine should surely have coolant a bit hotter than 65 degrees. Diesel engines run cooler because they are more efficient and more of the heat of combustion is turned into useful work; but petrol engines run hotter. If a petrol engine runs too cool, the combustion suffers, the engine corrodes and the oil gets polluted with unburned fuel and other hydrocarbons. I'm tempted to try blanking part of my radiator to get the temperature up a bit (10 degrees or so).

Mine runs at 65. The temp is not measured at the hottest part before you start playing with the radiator, and the fan doesn't kick in until just over 100!

Dave E

I should have been a little more accurate with my suggestion that 65 degrees is the normal working temperature. My assumption is that the temperature reading is taken from a coolant zone that isnt representative of the engine's head and block temperature. If you place your hands on the cylinders, after a decent run, you wont keep them for long. They are most certainly hotter than 65 degrees....... Ive been through the same tests that the author of the original question describes and came to the conclusion I now have. What finally satisfied my doubts was when I noticed a tank cam mounted on a TRX being ridden, on a Youtube clip, showing the temperature gauge at 60 odd degrees...... dont have any concerns with the gauge reading, your tests show that everything is spot on. Most certainly dont tinker with the radiator, you may cook the old girl. Cheers.

Thanks for this tread. I was fearing out thinking my engine was running too cool... then adversely wondering thy the fan never kicked in. 102-108 deg... I've just never got it that hot before!

You are taking the temp of the coolant itself as your temp sender is housed in the thermostat housing which is seperate from the motor.
85* is not uncommon for a little spirited riding but it serves the purpose to transmit the extra heat away from the motor itself. I am fitting a 10* lower valued thermostat fan switch myself, this won't make the engine run cooler but it will manage the temperature fluctuations better especially if you run a higher compression or do a lot of busy city traffic riding.

cobbadiggabuddyblooo wrote: I am fitting a 10* lower valued thermostat fan switch myself, this won't make the engine run cooler but it will manage the temperature fluctuations better especially if you run a higher compression or do a lot of busy city traffic riding.

That's a good idea. I'd be interested to know whether you are successful and which switch you end up using.

Honda accord 94-02 switch cuts in at 92 and and out at 87 from memory..

what size / fuel engine?