Fan Never Turns On When Riding or Idle

[obsessed]

Bike is a 1991 K75RT.  The problem I'm having is that the fan never seems to turn on when riding or when idle.  I've gone through most of the steps recommended here http://www.ibmwr.org/ktech/fan-diagnosis.shtml.  1) The fan is not seized 2) The fan turns on and spins when crossing the connectors at the switch under the tank 3) The temp light is functional (but has never turned on when riding) 4) the temp sensor tested within the normal range (when cold) when measured for resistance at the switch.   

No other problems with bike.  Starts fine.  Runs fine.  But, I just can't tell if the bike isn't getting warm enough to need the fan, or whether I've got a temp sensor problem, or possibly something electrical in between, or something else I haven't thought of yet.

I've only had it about since October 2015 and weather has been fairly cool up until now when riding, so at first I wasn't sure it was getting warm enough to need the fan, but now I've ridden in some 70 degree+ whether and still no fan.   

Any advice is greatly appreciated.  Thank you in advance!

[riots100]

I had a similar problem on my bike.  After going through the diagnosis that you linked, I later determined that the issues were both a bad Temperature Relay (in the Fuse/Relay box) AND a bad Temperature Sending Unit.  Replacing both fixed my problem.  The fan would finally go on if I left it idling long enough.  The bad Temperature Sending unit was also causing my brick to run rich as well.  It runs much better (with better milage) now.

[jakgieger]

These bikes are cool running.  Do you have a temp gauge?  My temp gauge has to be above 3/4 for the fan to kick on.  To get it to run, I get the bike hot, then put it on the centerstand and let it idle until the fan kicks over.  I had the problem of the fan stopping/seizing from lack of use. I did the manual override switchhttp://www.motobrick.com/index.php/topic,6702.msg45871.html#msg45871 so that occasionally I can run the fan.

[obsessed]

Thanks for the replies!  For clarification, my bike does not have the separate temp gauge, just the temp light that comes on.  I've considered doing the manual fan over ride, but my concern is that if the temp sensor or something has actually gone bad, it wouldn't really fix the problem, and could lead to something worse. 

[johnny]

can easily take half an hour or longer of idle for fan relay to make...

id make sure its full of coolant... gotts to burp it... then id fire it up... ride it for a while... let it idle till the fan comes on or till icoolant blows out the radiator cap...

im betting the fan will come on and you are good to go...

it took herseyb 5 beers for his fan to come on at 60 degrees ambient...

j o

[riots100]

Yes, it can take awhile.  I waited until the anti-freeze was boiling/blowing out of the overflow reservoir.  At that point the fan still hadn't come on, so I knew that something else was up.

[obsessed]

Hmmmmm... sounds like maybe I've been playing it too safe, not waiting long enough for the fan to turn on when idling after a ride.  Thanks!

[jakgieger]

I had to smell antifreeze before the fan would turn on...at the overflow tank .  That was why I did the override.

[Martin]

+1 fit an override it with keep the fan from seizing.
Regards Martin.

[jllphan]

Read that linked article again.  The part about testing the fan motor -- if you jump leads 15 & A2 and the fan doesn't come on (w/ the key switched on), then your fan motor is done.  I recently had the same issue, warning light worked, probe in spec, fan turned freely --but the motor was done.  Ordered a new one from Beemerboneyard and boom, it works.

[obsessed]

For those that have added the manual fan switch, using an old k-bike hazard switch has been recommended.  Does it have to be the hazard switch or will a used ABS or heated grips switch work as well?  Are they all SPST switches?

I'm asking because I haven't been able to find any available hazard switches.

Thanks!

[Martin]

Any switch will do.
Regards Martin.

[rbm]

Heated grip switch is SPDT-center off.  You can use one side of that switch.

[Scott_]

ABS switch won't work as it is not a maintained switch.....

[Laitch]

Hmmmmm... sounds like maybe I've been playing it too safe, not waiting long enough for the fan to turn on when idling after a ride.

By this time of year, it should turn on if you get into 20 minutes of stop-and-go traffic. If the temperature light comes on first, something is wrong. You can buy an automotive SPST switch for a fraction of an OEM switch's cost but you'll need to drill into something to mount it.

[kris]

For what it may be worth to this learned group I ended up going to a marine supply shop to get a weather-proof SPST switch. Couldn't find one at the usual car supply shops. 

[White Dog]

I got a 10 amp SPST rocker switch at Radio Shack for $3.49 and tax, to switch my power plug I use for my radar detector.  Mounted it on lower part of dash panel.