running too cool

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captainsteve
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Posts: 2
Joined: Sun Sep 22, 2019 8:11 pm

running too cool

Post by captainsteve » Fri Sep 27, 2019 1:51 am

I’ve had my trx for about 5 years and the temperature gauge always sits at about 60 degrees in normal riding and will raise up to 90/100 when sat stationary in hot weather where the fan cuts in and out.
It’s always bugged me that most vehicles I’ve had have run a bit warmer that this and you can usually expect any standard car or bike fitted with a temperature gauge for the needle to sit steady in the middle most of the time.
I’ve got more important things to worry about really but just recently on the way back from a long ride on an average speed limit motorway, looking at the clocks a lot, I decided I was going to put the problem to bed once and for all. I wish I hadn’t bothered now really but It’s been helpful reading the posts on here about the issue and so I thought I’d try and contribute a bit more to it.

*thermostat (marked 82 degrees) tested in boiling water with a glass thermometer that I believe to be fairly accurate:

Opens at 91degrees on rising temperature
closes at 81degrees on falling temperature

This seems ok to me when you check it against the specs in yamaha’s manual.


*strapped a digital thermometer to the thermostat housing with some heat transfer paste:
According to my digital thermometer, the bike is actually running around 70-80 degrees when the bikes gauge is reading about 60. If you let it idle until the fan comes on, the digital probe reads about 100 and the bikes gauge is on about 100. So, the bikes gauge seems to be not very linear.
With a hosepipe running over the radiator to cool it right down, I could not get the engine to run any cooler that 72degrees.

*Removed the clocks and the “thermo unit” and tested them against the specs in yamaha’s manual:
-thermo unit- 63ohm at 80 degrees, 33ohm at 100 degrees.
-should be- 47-53ohm at 80 degrees, 26-30ohm at 100degrees.

-temperature gauge- prepared a 50ohm and a 28ohm resistor to simulate 80 and 100 degrees on the gauge using a power supply. Found that the actual readouts on the bikes temperature gauge were 65 and 90 degrees respectively.

In summary. It would appear that my bike is running at the correct temperature and it is the instruments that are inaccurate. There doesn’t appear to be any provision for calibrating the temperature gauge. The needle doesn’t want to pull off and I can’t see anything els to adjust. I’m reluctant to pay £40 for a new thermo unit when the gauge might still be wrong and I dread to think what new clocks would cost.
I did try a cheap “universal” thermo unit off the net and the resistance is miles off (102ohm at 80 degrees and 58ohm at 100 degrees)

So after all this, I will continue to run around with my bike showing it is running cold. I just thought that this info might save someone a lot of work/expense. Or perhaps someone out there knows how to calibrate these gauges???

Trx envy
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Posts: 193
Joined: Tue Sep 18, 2018 8:16 am

Re: running too cool

Post by Trx envy » Fri Sep 27, 2019 2:21 am

Good post. I came to the same conclusion too, except with much less comprehensive and scientific approach. Basically just shot it with an I/R thermometer.
I tested the thermostat in a saucepan, it was fine, but swapped it out for an aftermarket one for a car that was rated to same temp but on testing openened slightly later. Also swapped out the fan switch. Stock from memory was 104c opening. I chucked a 95c in.
So it seems Yamaha were smarter than me after all, who would have thunk it lol. But at least the needle is staying off the stop when i ride and the fan comes on at a more civilised temp.
Ill be all ears if you work out a solution to calibrate the guages, but once you have waved the ir over it a couple times you know where it should and shouldnt be. Ive never gotten that hot but id bet that the red zone on the gauge is where it needs to be to let ypu know when you have a problem

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