Like the title says, I'm curious as to what a normal temp gauge reading should be. As in what position should the needle be once warmed up.

I just bought my bike and after it's warmed up, at idle the temp gauge needle is about halfway between the cold mark and halfway. So about 1/4 of the way up the range of the gauge.

But when I'm riding the needle is resting almost on the cold mark. I'm pretty familiar with automotive mechanics, and this doesn't seem normal to me.


So is this normal or no? And if it isn't normal, what is the most likely cause? The manual I have says the most likely causes of engine over cooling is a stuck open thermostat, a faulty radiator fan switch or a faulty thermosensor. The radiator fan seems to be functioning properly so I don't think it's that.

I doubt it would be the gauge itself either, or else it probably just wouldn't move at all.




Anyway, any help you could give would be great.

 

Naturally it's normal for the needle to fluctuate up and down within the range depending on conditions. That being said, there is a screw inside the gauge and my needle is usually resting at the bottom edge of that screw while riding and warmed up. We have 2 F3's, a 97 and a 98 and both of them are usually in that same position. The thermostat is responsible for regulating the temperature. Even if you had ice water in the radiator, the thermostat would control the flow of that ice water through the engine and maintain proper engine temperature. If it's running too cool while riding, then that's where I'd start with the thermostat.

 

Ok so update...

I went out and started it this morning, just let it idle and warm up. After about ten minutes the gauge was reading just below the screw in the gauge, and after a couple more minutes (and possibly revs) the needle was sitting over the screw, then the fan kicked on and it started to come down a bit.

Everything seems in order there.

But when I took it out to ride it, I didn't get a quarter mile down the road and the temp gauge was reading at the bottom on the range, just above the cold mark.




Since the fan comes on and off when it's supposed to, I doubt it's that. The thermostat doesn't seem likely either, as it's job is to quicken warm up time then open and allow the coolant to access the radiator, after that it's open all the time. If it was stuck open it would take an unusually long time to warm up, but once it is warmed up a stuck open thermostat wouldn't matter. After it is warmed up it's supposed to be open. That leaves he thermosensor, which doesn't make sense either, because if it was not functioning the gauge most likely would not move at all.


So I'm kinda stumped. My dad and my buddy are both telling me I'm nuts and that it is probably fine, but like IDoDirt said, the needle should be resting just below the screw in the gauge after it's warmed up.


I think I might go over to the bike mechanic today and just ask them, see if they can offer any insight.

 

my bike is a 1996 and the temp never gets over 1/4 and when running its just over the screw ,

i think its pretty normal never seen one at half when running along yet,

mine once nealy went to half in very hot weather and stuck in a traffic jam then when i got going it droped back to just under the 1/4 ,

dont worry about it,

 

The sensor is an analog unit and it may just be reading low.
It sounds like it's responding to temp fluctuation, so I doubt it's an issue.

If you are really concerned, get a in-expensive laser-pointer, digital thermometer.
Start the bike and start sampling. Get readings off the radiator (near the inlet/exit),
the block of the engine, the oil-cooler, and the big-fat radiator hoses.

The fan should kick on at about 180-195ish f, and the temp shouldn't be much over 240f maximum.

That should settle your concerns and you'll have a really cool laser device, as well.

Hope this helps, Ern

 

Well, I'm putting in a new battery (it's charging as we speak) because the lights would brighten when I blipped the throttle, then go dim when it returned to idle. Turns out the battery that was in it was 6 years old or so.

And sensors don't typically function properly without full battery voltage, so we'll see what happens with a new battery in it.

 

Actually a thermostat is working all the time. It is closed when heating and regulates the temperature at all times. it begins opening at XX degrees and is fully open by xx degrees. At any point in time during driving the thermostat will open and close a little more or less between open and close. as it reaches the low end it closes more, as it reaches the hotter end it will open. This will keep it at a somewhat steady temperature (notice your car does not move at all!) A stuck open thermostat will always run down to cold when coasting and/or driving. A stuck shut thermostat will always overheat. If your thermostat opens at 190, and while riding fast in neutral what happens if the temp goes below 190? Its going to close again, it doesn't matter if the engine is warming up or has been running all day.
My bike does the same thing, much less now that I replaced the thermostat, it was stuck all the way open. No harm in checking. Also could be air trapped in the system somewhere as well

 

This.

What you wrote described my bike's symptoms to a T, so I replaced the thermostat and that fixed it. Thank you, your advice was spot on and very much appreciated.