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Discussion Starter #1
Past few days I have noticed my cooling fans coming on when my temp gauge is not even at half. In the past I remember that the gauge would go nearly to the red before the cooling fans came on and the gauge would drop as the fans did their job. I just checked the overflow tank, and it is at the proper level. I ran the bike on the center stand until the fans came on, the reading was less than half level on the gauge, and did not change once the fans came on. I cleaned some of the bugguts off the radiators, but there wasn't that many anyway. Any thoughts on what may be happening here? When the fans came on there was pretty warm air coming from the side vents, so I am surmising the coolant is hot enough to need fans.....I did do a search and found some useful information, especially that the sender on the waterpump is the one that controls the gauge..
 

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Wrencher Extraordinaire
2005 K1200LT
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You may have a thermostat issue. The sender on the water pump does feed the gage but the one at the rear of the cylinder head is the one talking to the ECU and telling it to turn on the fans. One of them is lying or one of them is not getting the water flow.
 

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Discussion Starter #3
Could the cooling system be low on coolant and still have a quantity in the expansion tank?
 

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2005 K1200LT
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Yes. Idealy as it cools it should draw coolant from the tank to take up the space. The cap could have the valve stuck in it and not draw in the fluid. You can get an idea of how much is missing by squeezing the top cross hose and listening to the fluid (do this cold of course).
 

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Discussion Starter #5
Went out today and pulled the radiator cap to check for fluid, Yup full, was right at the top. Checked the connections for the temp sender at the pump, OK, started the bike, and let it idle, running the rpms up some to warm up the motor. It seemed to take an appropriate amount of time to get hot enough to make the fans kick in, maybe 6 to 10 minutes? I checked the hoses at the bottom and top of the radiators, and they seemed to get hot evenly, and were pretty toasty when the fans kicked in. The temp gauge never got above just below half, but I did notice a drop in the gauge when the fans kicked on. I continued to run the bike at varying rpms while parked, the fans ran, heat came out of the vents, the overheat light never came on, and the temp gauge never got higher. Maybe a bad temp sender? Anybody have an idea what the voltage values are for the sender, could I check it with a meter? Any other ideas? Could the thermostat be stuck open?
 

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2005 K1200LT
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I have one here I can go measure cold if that will help but I suspect it has gone bad.
 

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Discussion Starter #7
Thanks JZ, I thought I could use logic to determine the cause, but right now it escapes me......Like recently I thought I blew a head gasket on my Geo Metro (993cc's of raging glory) turned out it was a combination of waterpump and simultanious thermostat failure..made the radiator bubble like the HG was blown...fixed and running again 168K
 

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Discussion Starter #8 (Edited)
Trying not to beat a dead horse here, but I'm still not 100% confident in riding any distance yet. Yesterday I pulled the connector for the temp gauge and shorted it using a long wire so I could observe the gauge deflection on the dash. It deflected to full reading as I would have hoped, meaning the gauge is apparently not damaged. I did find an instance online that a K bike (an older one, not an LT)owner with a similar issue had determined that his sender was only dropping down to 96 ohms at running temperature, and another similar bike was dropping to 40 ohms at temperature. Unfortunately the 1 ohm scale on my old simpson meter is not working (ya can't put voltage through it!) so I'm unable to measure that low. My big concern is that maybe the head temperature is too high inspite of the water temperature....does the temp sender on the head read head temperature? or does it read the water temperature in the head? My concern is that there may be an intake leak that could be raising the head temperature, while the water temp remains within specs...A couple of recent events were, while at an estate sale about 2 weeks ago, I forgot to turn off the key and ran the battery down to the point of not able to start, had to jump it from a car, and the other about 4 days ago I was coming down a hill, and downshifting for the stop at the bottom, and when I pulled in the clutch to shift, the motor quit running, and restarted when I let the clutch out....not a normal occurrance for me. And a couple of more times that same run it seemed like it was going to quit running when I pulled the clutch for a downshift. I don't usually let things like that bug me as you hardly know what you are getting for fuel from a station these days...it may run great on one tank, and not so on another...I guess where I am now is 1. anybody know what the resistance of the water temp sender (the one on the water pump) should be at operating temp? 2. As I stated before, my cooling fans are kicking on at just under the half way mark on my temp gauge, where on the gauge are anybody elses fans kicking on at? Anybody have any thoughts about what could cause an increase of head temperature? HELP! I love riding my bike to work, it gets me started in a good frame of mind, and I know that when I get off, there is another ride home....for now I have to drive the GEO moto 4 wheel cage cycle....I just don't want to wreck the motor on the LT...Thanks in advance!
 

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2005 K1200LT
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It is in the cylinder head water jacket so it is reading water temp. FWIW my spare sender reads 664 ohms at room temp.
 

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Discussion Starter #10
Thanks JZ for sticking with me on this....I commute on my bike, and didn't realize how neurotic I would become if I was unable to ride it...Yea, it's an addiction...Anyway I thought I had done a pretty thorough search on the subject, but I guess it depends on what words you use on the search....I was doing another search and came across a post by Wallyo on May 4, 2011, who described the identical issue. http://www.bmwlt.com/forums/showthread.php?t=61162&highlight=temp+sender
He figured out it was the sender on the head to the Motronic unit that was bad, and was kicking the fans on prematurely, He changed out the sensor, and viola problem solved, back to normal. I have sent a pm to him to see if he had taken any resistance readings on the sensor so I could compare, but for now I am feeling like it is time for a new head temp sensor... :dance:
 

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casualemt said:
I am feeling like it is time for a new head temp sensor... :dance:
I concur. I had the same problem with the fans coming on - it was so bad they'd come on just moments after bike started. New sensor fixed her right up.
 

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I remember that post and now you have consensus from hallzee. Sounds like we have a winner here.
 

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Discussion Starter #13
Contacted Ride West in Seattle, they have a new sensor on hold for me, I'll pick it up Friday morning after I get off work, I'll post results...
 

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Discussion Starter #14
Ta Da! Picked up the new temp sensor Yesterday at Ride West BMW, came home and started pulling plastic, removed ignition coil, and used a 19mm wrench on the sensor, just a tip, I put the new sensor right next to the installed old one, ( theres a bracket it can lay on) so when I unscrewed the old sensor, I held my finger over the hole and shoved the new one right in, only lost a little coolant. PITA was routing the wiring around the big aluminum frame member as the wire on the sensor is just long enough to reach the plug if it is routed just right, had to do it a couple of times to get it to reach..the other PITA was the plug is under the small rear plastic cover, and I couldn't see how to get the grab handle off so I could pull that plastic. I looked through the chapter in the Clymers, but didn't see any mention of how that thing came off, ended up pulling the screws for the plastic, and putting a little wedge at the bottom to hold it out while I used some long forceps to get the plug in and put on the clip. Other than that it was pretty straight forward, dismantle half the bike, remove and replace a million screws and bolts using various wrenches, and 5 different screwdrivers. Of interest was I unscrewed the cover on the head between the cams that says BMW on it, to allow me to move the spark plug wires and the ignition coil, and it looked like a couple of the wires may have been shorting to the cover...I put some electrical tape over the areas on the plug wires that looked like they may have been shorting, and will be ordering a new set soon...Otherwise, fired the bike up, test ride, rode it to work this morning, ALL IS NORMAL!!! no more fans running at operating temp... :dance:
 

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2005 K1200LT
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Wooh Hoo!

Glad you got it solved.
The grab handle has two 5mm allens holding it. One on top under the seat and one in from the side.
 
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