Cooling fans start up before needed - K-Bikes.com - Excellence in Motion
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post #1 of 14 (permalink) Old Aug 15th, 2008, 12:44 pm Thread Starter
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Cooling fans start up before needed

Hi All,

I have a 2000 K12RS with 37,000 miles. Recently, the bike has been acting differently. Both fans start up when temperature gauge hits 1/4 full scale. Lately it's been cool in PA and I've noticed that the fans kick in within the first 1.5 miles from when I first start out in the morning. I suspect that my sending unit is changing states much too early. It seems to be getting worse. It began to start the fans when it reached the "normal" level but now they start not long after the gauge starts moving from cold.

My dealer stated that the sending unit was tested and it is okay but I wonder if they tested when it closes. Are there any other components in the circuit that could cause this condition? They replaced a faulty radiator cap but this did nothing to correct when the fans kicked in.

Does anyone know the part number and approximate cost of the sending unit? Where is it located on the engine? Is it a simple swap or must I remove a lot of engine parts to get to it? Do I need any special tools? What website could I order this part from that is reputable?

I appreciate your help and suggestions..
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post #2 of 14 (permalink) Old Aug 15th, 2008, 2:58 pm
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I believe that item #15 is what you are looking for. It is located on the lower right side near the front of the water/oil pump. Remove the belly pan and you can see it at the right front of the engine. http://www.webparts.com/diagram.php?...66&hg=11&fg=35

You can buy it here from Hammersley BMW or from Chicago BMW.

When the fans come on, do they both blow hot air??

Bruce C
'04 K1200RS Capri Blue(totaled)
2008 Triumph Sprint ST
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post #3 of 14 (permalink) Old Aug 16th, 2008, 7:56 pm Thread Starter
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Bruce,

Thanks for the quick reply. Are there two sending units, one for the fans and one for the temp gauge? When the fans first kick in, they blow very mild warm air. After I drive for a few more miles, they blow the "normal" hot air. So it does support that the fans are starting too early rather than the temp gauge being wrong.

I wasn't sure how the circuit works on my model. Now that you pointed me in the direction of where it is located on my engine, I'll have to check out the connectors as well. Perhaps they might be getting corroded, which would vary the resistance. It's not randomly starting the fans. They come on every time at 1/4 full scale so I know it's not a lose or broken wire.

Is there a way to test the sending unit? Is it worth the time to put it in a pot of heated water to determine the temperature where it changes state? I'm not sure if it's just a switch that opens and closes or is it an analog signal that varies with temperature?

Thanks for your help. I appreciate it. My K12RS is my daily driver and I don't want to burn out the electric motors by having them run constantly after the first mile.
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post #4 of 14 (permalink) Old Aug 16th, 2008, 9:28 pm
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Here is a pdf of an '04 KGT oil/water pump.
The oil pressure switch has been moved in relationship to a 2000 model. But the temp sw.(item #17) is in the same place!


I would identify the water temp. sensor by the pictures. You could try grounding the sensor wire with the ignition key on. The fans should start when the wire is grounded.

And I wouldn't waste my time with a water test on the old sensor. I think if your fast enough you could swap sensors without spilling much coolant at all.


I believe the temp. gauge sensor is located on the rear of the cylinder head.
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Bruce C
'04 K1200RS Capri Blue(totaled)
2008 Triumph Sprint ST
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post #5 of 14 (permalink) Old Aug 17th, 2008, 12:05 pm
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There could be a few mistakes in this thread, unless the later bikes had some big changes. Here's how my '97 works:

The sensor which is fitted in the bottom of the water pump housing only drives the temperature gauge.

The sensor at the back of the cylinder head tells the ECU about the water temperature so it can apply the right map when cold/warm. This is an important item. At the same time the ECU reads this sensor it triggers the fan relay. So it's the ECU controlling the fans with input from the cyl. head sensor.

Since the gauge and fans are on separate sensors they can both do different things - the gauge reading could be wrong and the fans cut in at the correct engine temperature, or the gauge is correct and fans cut in at the wrong temperature. The latter case is more serious because it means the engine map and cold start will be upset.

When the bike runs at cruise in not too hot weather, does the temp gauge hold steady at about 1/2 way. If it does this suggests the gauge is OK. If the gauge is reading low say 1/4 when the fans come on, that suggests the gauge sensor in the water pump is faulty. Also if you feel the radiator header tanks they should both feel quite hot when the fans cut in. If they feel cool and the gauge reads 1/4 then the cyl head sensor sounds faulty.

Now for the scientific stuff. I removed both sensors on my '97 K1200RS when the motor was out of the frame and measured the sensor charactersistics. Yours is a later bike so you may not get exactly the same values. But some information is probably better than none so I've attached my results in table form. If you want the XL sheet, PM me. Notice that the two sensors have quite different characteristics.

One final variable is the water thermostat which should be fully open at around 85 deg. C.



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Last edited by voxmagna; Aug 17th, 2008 at 12:12 pm.
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post #6 of 14 (permalink) Old Aug 17th, 2008, 2:34 pm
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Quote:
Originally Posted by voxmagna
There could be a few mistakes in this thread, unless the later bikes had some big changes. Here's how my '97 works:

The sensor which is fitted in the bottom of the water pump housing only drives the temperature gauge.

The sensor at the back of the cylinder head tells the ECU about the water temperature so it can apply the right map when cold/warm. This is an important item. At the same time the ECU reads this sensor it triggers the fan relay. So it's the ECU controlling the fans with input from the cyl. head sensor.

Since the gauge and fans are on separate sensors they can both do different things - the gauge reading could be wrong and the fans cut in at the correct engine temperature, or the gauge is correct and fans cut in at the wrong temperature. The latter case is more serious because it means the engine map and cold start will be upset.

When the bike runs at cruise in not too hot weather, does the temp gauge hold steady at about 1/2 way. If it does this suggests the gauge is OK. If the gauge is reading low say 1/4 when the fans come on, that suggests the gauge sensor in the water pump is faulty. Also if you feel the radiator header tanks they should both feel quite hot when the fans cut in. If they feel cool and the gauge reads 1/4 then the cyl head sensor sounds faulty.

Now for the scientific stuff. I removed both sensors on my '97 K1200RS when the motor was out of the frame and measured the sensor charactersistics. Yours is a later bike so you may not get exactly the same values. But some information is probably better than none so I've attached my results in table form. If you want the XL sheet, PM me. Notice that the two sensors have quite different characteristics.

One final variable is the water thermostat which should be fully open at around 85 deg. C.
I will defer to Vox on which sensor operates which device. He has first hand knowledge on these sensors.

Bruce C
'04 K1200RS Capri Blue(totaled)
2008 Triumph Sprint ST
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post #7 of 14 (permalink) Old Aug 19th, 2008, 2:13 pm Thread Starter
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Vox,

Thanks for the detailed explanation. When I am riding the bike, the temperature gauge runs where it always did. It's right around the halfway point (50% full scale). It climbs to temperature normally as well. When the fans kick in, there is not much heat blowing from the radiators.

It sounds like a faulty sending unit from the cylinder head maybe causing me these problems. I am also experiencing slight surging when running at a constant speed. I wonder if the two are related if the mapping is off........ I just hope it's not the ECU...

If I wanted to replace the rear cyl head sending unit, would it be a big job? How hard is it to get to this sensor? Any special tools needed that would stop me in my tracks?

I appreciate your help!

2000 K1200RS - Blue/Silver
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post #8 of 14 (permalink) Old Aug 20th, 2008, 10:27 pm
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Cooling Fans

Generally, when the coolant sensor has failed the fans run all the time. You have probably located the sensor by now. It's lead runs behind the left "battery" cover and should be zip-tied to the frame just below the seat on the left. You can test it with an ohmmeter. To replace it, unplug the lead and snake it out so that it is hanging from the sensor. Unscrew the old sensor and quickly thread the new one in-you'll lose very little coolant.
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post #9 of 14 (permalink) Old Aug 21st, 2008, 12:01 am Thread Starter
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I haven't had the chance to tear into the bike just yet but thanks to your description, I will attempt to locate it this weekend. I'm a bit concerned now that you mention that it usually fails with leaving the fans run all the time. That is not the case with my bike. If not the sensor, what else could be causing this issue? Could the program in the ECU need to be reflashed? The only other "odd" thing that occurred about the same time was once when I pulled off the road to get something out of my sidecase, I turned off the bike (needing the key for the case lock). About 3 to 4 minutes later, I jumped back on and when I tried to start it, I heard a crack and the bike didn't start right away and almost lost total power for about 1/4 mile. The faults that I'm seeing now started after that occurrence. Does this relate somehow to the ECU or sensor?

2000 K1200RS - Blue/Silver
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post #10 of 14 (permalink) Old Aug 21st, 2008, 11:16 am
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Failure isn't quite the right word. Apparently if you disconnect the wire to the Cyl Head sensor, the ECU defaults to fans run continuously. Neat testing tip.

K-bikes aren't like PC's although they have processors in them. Firmware is proprietary and some of the older memory chips are so old you'll struggle to get blanks and a reader that accepts the chip.

But first you have to get inside the ECU box and that's not so easy. If you break anything along the way, then fixing a fan sensor is nothing compared to an ECU and it stops you riding! Check the price of a replacement ECU first before venturing into this territory.



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