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Temperature Light coming on

7K views 19 replies 11 participants last post by  heffly 
#1 ·
Me and the wife took a little ride today. About 100 miles from home, the temperature light came on. We were going about 75. I cut the throttle and pulled in the clutch and coasted with the engine idling and the light went out after a few seconds. It happened again a couple more times, about every 5 miles or so. I cut the throttle and pulled in the clutch and each time it went back out after 6 seconds or so of coasting. I pulled into a store and got a bottle of distilled water and topped off the overflow tank, it just took about a half pint to fill it, and we stayed a while and let it cool down. Headed home again on the freeway going about 70, after about 15 miles it came on briefly a couple of times, like before, going out after coasting a short piece. I got off the freeway and we did the last 45 miles on a side road going 50 to 55 and the light never came on again at the lower speed until just before I pulled in the driveway, it came on and went right back out after a second or so. This is the first time I've ever seen the temperature light come on. There is not, and has never been any indication of coolant loss and I changed the coolant summer before last, and I can't tell if the fan is coming on or not when riding. I'm wondering if the fan isn't coming on when it needs to ?

It's on 03' 1800R with 36000 miles on it.
 
#4 ·
The fan does not run at 70MPH, the air blowing through the radiator cools the coolant.
It runs in stop and go traffic for the most part or at low speeds, other 1800 owners could
provide better info. My 1300 fan never runs at speed.

The coolant recovery tank is not an indicator of what the coolant level is in the engine.
The coolant when it gets hot and expands then goes to the recovery tank through the radiator cap and a hose.
When the engine cools and the engine coolant has a negative pressure compared to the outside it will draw coolant from the tank back into the cooling system.

If there is any leak or loose fitting on the recovery hose it can allow coolant to flow to the recovery tank
but it will suck air into the cooling system when the cooling system cools down. Engine can get low enough in coolant to run hot.
Coolant level has to be checked at the radiator cap under the fuel tank.
Prop up the tank and check..
 
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#5 ·
I agree with Hans.. My fan never runs at highway speed, only when riding around town or setting while idling..
First check the coolant level at the cap when engine is cold.. If it's completely full check for restrictions, like a stuck t-stat or partially plugged radiator.
 
#6 ·
Correct the fan only comes on when air is not moving through the rad, like at stoplights. Test your coolant, when was the last time you changed the coolant? Have you tested your thermostat? Have you ever changed your thermostat? Have you popped the rad cap off to check the system, not the reservoir?
 
#7 ·
With the outside temperature in the high 50's yesterday, the air flowing across the radiator was pretty cool going down the highway. I did change out the coolant 18 months ago. I have never changed out the thermostat, and I was unable to pull the tank off yesterday, just trying to get home. Ill pull the tank off in the next day or two to get to the rad cap and check the coolant there. That's something I usually never look at. Probably just low on coolant but Ill start there. Thanks for all the suggestions.
 
#8 ·
Last year on the trip out west i did have my fan coming on occasionally while riding at 70 mph. I finally decided it was because I had about a 30 mph tail wind, maybe more..lol. That was the only time it came on at speed though.....mostly just when im under 40 mph....or so stopped.
 
#9 ·
IS the bike actually getting hot ? I Agree with Papa. Pull the tank and remove the thermostat and test it. Another possibility is a ground wire
 
#10 ·
The sensor for the temperature light isn't the same one that controls the fan. If the OP pulls the thermostat for testing he can also remove the sensor and have that tested too since it's mounted in the same housing.
 
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#11 ·
Fan comes on @ 215 degrees and goes off @ 206 or there abouts. In Florida in takes about 10 min of idling. Running temp of the bike on the road is about 185 degrees. My fan comes on often at large intersections in the summer. I installed temp gauge on mine.
 
#16 ·
As much of a PITA it is to check, the coolant level needs to be checked periodically. I suggest the next time you take a decent ride make a note of the coolant level in the reservoir tank while the bike is still hot. Check it again the next morning and see if it's gone down. This at least tells you if the engine is sucking the coolant back in that was displaced by expansion during your ride.
 
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