Cooling Fan not coming on

Mikexup

Joined
Sep 25, 2018
Messages
9
Age
73
I thought the bike might be running a bit warmer than usual the other day when I went for a ride. Today I had a puff of vapor that only lasted a couple of seconds then the fan came on and cycled perfect. Took the bike for a ride and again bike ran warmer at the end than it did at the beginning. Stopped the bike and checked the fan, nothing. Should I check a sensor first, or is it the fan since there was a vapor, (didn't really smell like electrical) and take for granted it is the fan. Bike: 93 ST1100. Thanks for any help.
 
easy to check sensor, just pull the connector off the sensor and ground the wire to the engine/frame. If the fan comes on then the sensor might be bad, but you also want to verify your coolant level is high enough that the sensor is immersed in enough coolant to work properly.

if the fan doesn't come on after grounding the wire then you'll need to trace out the 12v supply to the fan, or check the fan itself for problems.
 
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"a bit warmer than usual" is a bit vague. On my ST1100 I don't think the fan ever came on when I was moving. The needle had to get above the 50% point by a fair amount before the fan came on while sitting at a traffic light.
  1. How far up the scale was the needle when you checked the fan and it was not running.
  2. Curious about the "vapor". Coolant will normally have a very sweet smell to it, at least that is how I would describe it. I once had that smell while idling and quickly found that I did have a coolant leak, although it was quite minor. If you do have a leak, it could all be evaporating without you even seeing the evidence, but you might smell it. If it leaks down enough, your fan switch will not cycle the fan properly because the coolant level is too low for it to read.
edit: I see dwalby beat me to it. What he said! :)
 
I agree with all the above. I experienced the same problem last summer. The coolant level was correct in the expansion tank but the rubber pipe that joins the neck of the radiator had a long split at the top. Apparently this leak is quite common with age.
 
Thanks for the help everyone. After doing the test on the switch the fan does come on, so thankful for that. Is Honda the only on who makes the new switch? I saw some post having to do with a NAPA part, but I think this had to do with the thermostat.
 
As previously mentioned, and before replacing the switch, make sure the hose going down to the expansion tank is not split as it comes off the thermostat housing. When split, it spits coolant when warm and sucks air when cooling off. This is much more likely than a bad switch. Also, the fan will not come on until about 12:30 on the temp gauge, and will usually shut off in a minute or so. Good luck.

Curious, what do you mean about a "puff of vapor"? Heard, smelled, saw? Maybe this was from the hose split?
 
That's interesting, since I did have a puff of vapor or smoke but didn't smell like anything electrical. Is the tube something that's easy to check or do you have to pull panels off the bike to see it and check things out?
My bike never went above a quarter off the cold mark, and the cooling system held it there by the fan coming on in intermittent spurts.
Spitting coolant...never had a drop of anything on the floor or fairing but would still like to check it out. Hopefully this is a simple fix.
 
Look under the front of your bike. You will see the radiator cap and the thermostat housing. Notice that long hose skinny hose coming from the filler neck housing? Check that hose for cracks. Last year I was fighting a heat problem on my bike. Changed fan switched, antifreeze flush fill X 2. Fought it all summer long.....even took it to a Stealer only to tell me it is functioning normally. My problem was the heat off the motor on my shins and legs.
 
Start where a mechanic would start, check coolant level, in the radiator and over flow tank. Inspect the overflow hose and fitting by the radiator cap. Now if that,s all good we can move on to other checks. My over flow hose and fitting were plugged with dried anti freeze. Then upon further inspection found the 2 hoses under the carbs has very slight seepage and the hose ends had signs of corrosion:think1: You did say the fan was working... lets fix something that's working
 
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Totally agree that it's too early to start buying parts...you'll need to check coolant and hoses, and once all is good, you need the temp gauge to go past "12 o'clock". This typically happens if you just let it idle for a while...only then can you assess if anything is wrong with the sensor and/or fan
 
Mikexup said:
That's interesting, since I did have a puff of vapor or smoke but didn't smell like anything electrical. Is the tube something that's easy to check or do you have to pull panels off the bike to see it and check things out?
My bike never went above a quarter off the cold mark, and the cooling system held it there by the fan coming on in intermittent spurts.
Spitting coolant...never had a drop of anything on the floor or fairing but would still like to check it out. Hopefully this is a simple fix.
Click to expand...

IME, you need to pull some tupperware to get to the radiator cap and that hose. Odd that it never went above the 1/4 mark... that's where mine normally runs when up to speed. If I'm in stop/go traffic, it goes just past 1/2 way and then the fan comes on to drop it back to 1/2. The fan should not come on until just after the 1/2 mark. I wonder if someone replaced your switch with a lower temp one? The coolant 'spit' is very small and you likely won't see it drip, just a slow loss of coolant in your expansion tank until it's empty.

From cold, I would start it on the center stand and monitor the gauge, when the fan comes on and goes off. Let it cycle 3-5 times and see if it's repeatable.
 
paulcb said:
Odd that it never went above the 1/4 mark...
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very odd, possibly caused by too much air in the system so the temp gauge wasn't reading properly. Agree with everyone else that checking the level in the radiator is the next step, anything else is a waste of time until that variable is known.
 
Mikexup said:
That's interesting, since I did have a puff of vapor or smoke but didn't smell like anything electrical. Is the tube something that's easy to check or do you have to pull panels off the bike to see it and check things out?
My bike never went above a quarter off the cold mark, and the cooling system held it there by the fan coming on in intermittent spurts.
Spitting coolant...never had a drop of anything on the floor or fairing but would still like to check it out. Hopefully this is a simple fix.
Click to expand...
+All they said, the only panel you need off is the right grey panel with the locked compartment. But obviously the tank cover will have to come off too, I think. Be careful don't pull at it, there's hidden screws everywhere. You need this off to get the cap off anyhows. I replaced this expansion tube this year, easy peasy but get new clips too, the old ones will be buggered. It usually cracks where it bends out of the thermostat housing and be aware the ABS and non ABS are different. Sorry if I've repeated anything. Good shout about low coolant and temp gauge.
Good luck.
Upt'North.
 
Upt' North said:
+All they said, the only panel you need off is the right grey panel with the locked compartment. But obviously the tank cover will have to come off too, I think. Be careful don't pull at it, there's hidden screws everywhere.
Click to expand...
it sounds worse than it really is, but here's what needs to come off to get unobstructed access to the rad cap

  1. remove both saddlebags
  2. remove both sidecovers
  3. remove seat
  4. now you can access the 4 bolts that hold the topcover (gas tank looking thing) on and remove it to get access to the cleverly hidden screw for the right side grey panel, but don't get too excited just yet.
  5. remove the right side engine access cover (like you're changing spark plugs)
  6. now remove all the screws that hold the grey panel in place and remove it, the cap is now visible
 
dwalby said:
it sounds worse than it really is, but here's what needs to come off to get unobstructed access to the rad cap

  1. remove both saddlebags
  2. remove both sidecovers
  3. remove seat
  4. now you can access the 4 bolts that hold the topcover (gas tank looking thing) on and remove it to get access to the cleverly hidden screw for the right side grey panel, but don't get too excited just yet.
  5. remove the right side engine access cover (like you're changing spark plugs)
  6. now remove all the screws that hold the grey panel in place and remove it, the cap is now visible
Click to expand...
How can my memory be that bad, I only did it in March. Don't answer that it was rhetorical.
Ta Dwalby.
Upt'North.
 
The fan's thermo switch is located pretty high up on the radiator. The fan not activating is a classic sign of the split overflow line as well as a normal appearing coolant level in the overflow tank. What will typically be found is that the radiator level itself is low when removing the cap and looking in there. Don't open the cap when the engine is hot though - safety first! The switch will not activate properly if the coolant level in the radiator drops below the switch's location.
 
Thanks to everyone who replied, and yes it was a split hose about a inch coming off the radiator and where it makes the sharp bend. I had already put a thermal switch in and the fan was working but still not keeping the temp as low and as consistent as before. Since it was going to rain today anyhow, thought it was a good time to start taking plastic off.
Dwalby a special thanks for your simple instructions, it made things a lot easier knowing exactly the next step. Thanks Again guys.
 
Mikexup said:
Thanks to everyone who replied, and yes it was a split hose about a inch coming off the radiator and where it makes the sharp bend. I had already put a thermal switch in and the fan was working but still not keeping the temp as low and as consistent as before. Since it was going to rain today anyhow, thought it was a good time to start taking plastic off.
Dwalby a special thanks for your simple instructions, it made things a lot easier knowing exactly the next step. Thanks Again guys.
Click to expand...
Glad you found the 'split' hose and repaired it.
Have a good summer.
 
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