Replaced cooling fan...It still won't turn on

[Wheezyryder]

Still in the process of getting my new-to-me '85 K100 running. After getting a fuel leak fixed, I finally took it for a test ride. Starts, runs, idles, shifts and stops great. Had several electrical issues that I'm still working on getting sorted out. The most important one is that the cooling fan doesn't turn on when it should. I ran the bike a couple of miles down the interstate on a fairly warm day (85F). Got off the exit and got stuck at a stop light for several minutes. After a couple of minutes the coolant temp light on the instrument cluster came on (I don't have a temp gauge just the dummy light). Soon after I got moving again the light turned off. When I got home, I let the bike idle for a couple of minutes until the temp light came on again and confirmed that the cooling fan is not switching on.

Things I've already done to try to fix it:
-Battery 2 months old and fully charged (reads 12.82 on the multimeter).

-Replaced the fan with a Spal fan. The original fan could be spun with your finger, but had more friction that I thought was normal. When I removed it and connected it straight to 12V and ground, it ran intermittently and made a lot of noise. It was also missing 2 of the fan blades. Figured it should be replaced even if that isn't why it's not turning on.

-Cleaned the electrical connections at the fan, the temp sensor at the radiator and the temp relay under the seat. In fact I've cleaned most of the electrical connections on the bike so far. A few of the electrical gremlins I found on the first ride were fixed just by cleaned connectors. I didn't use Deoxit, since I already have a can of CRC electrical cleaner.

-Cleaned the ground connections at the transmission case and to the frame just behind the handlbars. Cleaned the mounting points and ring terminals to shiny clean metal with die grinder/Dremel and wire wheel.

-Replaced all fuses with new fuses.

-Connected the 2 leads at the temp sensor using a jumper wire as recommended by the Clymer manual. Fan didn't come on.

I also found this troubleshooting guide on the IBMWR page.

https://ibmwr.org/index.php/2007/06/01/cooling-fan-diagnostics/#:~:text=The%20simplest%20test%20of%20the,this%20longer%20than%2015%20minutes

It gives a pretty detailed guide on how to diagnose cooling fan issues. It details a series of tests to be performed from the plug at the fan relay under the seat. I'm not incredibly savvy with electrical stuff so I'll take all the help I can get. My results from this testing are as follows:

      -Temp probe resistance test- Got 3400 ohms on a cold test. A bit higher than the range the author of the article talked about but not by much.

      -Temp warning light test- I connected the to leads with a jumper and the temp light did not come on. I have seen the temp light come on while riding so I'm not sure
        what to make of this result.

      - Fan motor test- I connected the 2 leads with a jumper wire and the fan did not come on. Tested the brand new fan by connecting it directly to 12V and ground and it
        did come on. Tested for voltage at the fan connector with the jumper in place and got nothing. Visually inspected all of the wiring between the relay box under the
        seat and the fan connector. Kinda hard to trace as it disappears into the wiring harness but no obvious damage.

Apologies for the long post. I did my best trying to figure this out on my own but I'm out of ideas other than the rather expensive option of throwing new parts at the problem. Anyone have any suggestions for other things I can check?

[Laitch]

Have you flushed the old coolant out of the system then replaced it with new coolant, filling the system by scrupulously following BMW's instructions?

[Wheezyryder]

Laitch- After the first ride I did drain the system in order to check the thermostat (which seemed to work just fine when tested in hot water). Refilled with distilled water and a radiator cleaner/flush product and rode it again with the same result. Drained that and rode with just distilled water after that to rinse out the cleaner. Same result no cooling fan engagement. I did my best to burp air bubbles out of the system each time by filling slowly and rocking the bike back and forth/ side to side but did not scrupulously follow the procedure in the Clymer manual. I planned on doing that when I refilled the system with the proper coolant for the final fill. Could dirty/old coolant and/or air bubbles in the system cause the fan to malfunction?

Currently the radiator is still off the bike from installing the Spal fan. I thought it would make electrical troubleshooting easier with the radiator out of the way. Oil/water pump is also currently disassembled awaiting parts in the mail. I'm rebuilding that as preventive maintenance since I don't want to rely on the 36 year old original seals to do their job.

[Laitch]

I did my best to burp air bubbles out of the system each time by filling slowly and rocking the bike back and forth/ side to side but did not scrupulously follow the procedure in the Clymer manual. I planned on doing that when I refilled the system with the proper coolant for the final fill.Could dirty/old coolant and/or air bubbles in the system cause the fan to malfunction?

I think you're wasting your time by not completing the coolant change appropriately. Straight distilled water shouldn't be used. You've change out the fan and know that it's working. If the radiator core has been cleaned, mount the radiator in the frame and refill with 50:50 or 60:40 coolant to water ratio depending upon the winter temperatures where the moto is located. Follow the coolant replacement instructions in the BMW K75/K100 2V manual downloadable from this site. Always follow instructions scrupulously. Avoid extemporaneous procedure modifications until you have more understanding.

Low coolant and air in the system will cause overheating and the fan might not be able to mitigate it even if it is working.

I'm just trying to understand what you've done. I don't know how you've tested what you've tested because you don't describe your method. The fan won't start in a test if the correct connections aren't made. Also, the fan won't start if the temperature relay isn't functioning correctly from internal flaws or wiring defects connected to it but that doesn't mean you should buy a replacement right now.

[Wheezyryder]

Laitch- I didn't do a full, proper coolant change per the manual because I was doing a cooling system flush per the manual. That's why I filled and ran it with straight water. The only part of the procedure that I omitted was to remove the fuel tank after running it to check/top off the coolant. Admittedly, I used the Clymer manual because a copy of it came with the bike. The Clymer procedure for a drain/flush/fill sounded like the same procedure for a cooling system drain/flush/fill that I've done on other motorcycles and autos. I just looked at the procedure in the BMW manual and it seems to be the same. I fully intend to fill with proper coolant/water when I reinstall the radiator. But I think that all the components of the cooling system are working well except the cooling fan. The bike is able to maintain temp within range to keep the temp light on the gauge cluster from coming on when it is moving and has air flow. It is only when it doesn't have air flow that the problem arises. I feel confident that once I get the fan working I won't have a problem.

Apologies for not being more detailed about the electrical testing procedure I followed. The link I posted to the IBMWR resource was very detailed and I followed it closely. It was written by a fellow named Jeff Dunkle who seemed to be very familiar with the K bike electrical system. It is the only troubleshooting resource I've found, as neither the BMW or Clymer have much on the subject. I'll paste a copy of his procedure below. I'm getting some abnormal test results and I'm just not sure where to go from here to get the fan working. Here's the procedure he wrote up:




Idle Test:
The simplest test of the system is to start the bike, let it idle, and listen for the fan to come on. My experience is that if it’s going to work, the fan will come on at about 8 to 10 minutes of normal idle. This worked for me testing K75S and one K100. I’d be uncomfortable doing this longer than 15 minutes. One bike I saw that was left to idle for about 25 minutes (and was subsequently was found to have a bad fan circuit) “blew it’s guts” after about 25 minutes of idling by spewing half it’s coolant out of the over flow tank filler.

Tests that can be run from the relay connector under the tank:
The fan relay (switch per BMW?) is located in the “relay box” under the rear of the gas tank, in the middle of the right side. Its a whitish color. Remove the mount screw, lift the relay and disconnect the connector plug on the base. There’s a contact chart on the side of the relay that corresponds to the tabs on the base of the relay. The following is a chart for the connector using the same numbers, mirror imaging connector chart from the relay/switch. These connection labels correspond to those on the Owners Manual wiring chart. I’ve confirmed most of these connections with wiring checks.

Female connectors plug

              (molding ridge)------\
                          __________^_________
     Key:                |                    |
                         |  |(E)   []    (9)| |
     | (female           |                    |
         connector)      |                    |
                         |        (15)        |
     []  (empty slot)    |  |(A2)  __  (A3) | |
                         |                    |
                         |        (31)        |
                         |  []     __      [] |
                         _____________________

Components attached to each connector:
E  - temperature sensor
9  - goes somewhere that looks eventually like fuse #6
A2 - fan motor
15 - fuse #7
A3 - Overheat light
31 - ground
These tests can be run by using a multi-meter and/or jumper wire on the various connector terminals to the relay/switch for the fan.

Temperature probe “test”:
Measuring the resistance between E and 9 will read the resistance of the temperature probe. “Normal” cold bike readings I’ve seen are (+-) 2,200 ohms. On colder days, closer to 3,000 ohms. If you warm the bike up, quickly remove the tank and take a reading, expect to see about 520 ohms. Readings in this range cold and hot seem to confirm normal temperature probe function.

Over Temperature Warning Light test:
With the key turned on, touching a jumper wire to connectors 31 and A3 should turn on the over temp. warning light. If not, check fuse 7, the light itself, then wiring between it and the relay box.

Fan Motor Test:
With the key turned on, touching a jumper wire to connectors 15 and A2 should turn on the fan motor. If not, further test of the fan is needed. What I’ve done in the past is unmount the radiator enough to expose the fan and loosen the connector plug. First measure the resistance through both leads in the fan connector. You should see a very low reading, about 3 or 4 ohms or so. Next jumper 12 volts to the colored wire connector and ground the brown connector wire. The motor should run. If not, it’s probably burned out or has damaged brushes. I saw one motor with the brush housing totally melted.

If it does run, next measure the voltage coming out of the plug supplying the fan. To do this, turn on the key, put a jumper from connectors 15 and A2 at the relay plug, then connect your multi-meter to the fan power plug, red to colored wire connector, black to brown wire. You should read 12 volts. If not, you have a wiring problem or blown fuse. Start by checking for 12 volts at connector 15 (thanks to Dimitri Likissas for this tip).

Clymer suggests testing the fan/system by disconnecting the temperature sensor plug and jumpering the connectors. With the key on, this, they say, should turn on the fan motor. I’ve not done this test yet and cannot speak to it’s validity. It would introduce a zero resistance into the sensing circuit in the “relay”, which is probably OK. This would test both the relay, fan, and associated wiring. It’s much easier to remove the tank and get to the relay box than access the temperature probe.

[The Mighty Gryphon]

Please forgive me, I can sometimes be very easily confused, but are you running the engine without the radiator?  I seem to see you saying that the radiator is not on the bike while you work on the fan.

[alabrew]

Over Temperature Warning Light test:
With the key turned on, touching a jumper wire to connectors 31 and A3 should turn on the over temp. warning light.
If not, check fuse 7, the light itself, then wiring between it and the relay box.

Did you do this?

You posted: Fan motor test- I connected the 2 leads with a jumper wire and the fan did not come on. Tested the brand new fan by connecting it directly to 12V and ground and it did come on. Tested for voltage at the fan connector with the jumper in place and got nothing.

This seems to be a clue too. You know the fan is good, so it has to be the wiring or what turns it on and off.

Did you - next measure the voltage coming out of the plug supplying the fan. To do this, turn on the key, put a jumper from connectors 15 and A2 at the relay plug, then connect your multi-meter to the fan power plug, red to colored wire connector, black to brown wire. You should read 12 volts. If not, you have a wiring problem or blown fuse. Start by checking for 12 volts at connector 15

[alabrew]

TMG, I took it that he just was testing the fan, not running without it. He was flushing too.

He isn't riding it "Currently the radiator is still off the bike from installing the Spal fan. I thought it would make electrical troubleshooting easier with the radiator out of the way. Oil/water pump is also currently disassembled awaiting parts in the mail.

[The Mighty Gryphon]

I really need new reading glasses.  When confronted with dense text, I have some trouble getting all the words in the correct order, and sometimes I will skip a line or read the same one twice. 

[Wheezyryder]

Gryphon- haha no sir! Sorry for my long-winded posts. I definitely did not run the bike without the radiator attached. I could see how that might potentially cause overheating! After running it a few times to flush the radiator and confirm that the cooling fan isn't turning on, I removed the radiator to install the Spal fan. Still have it off because it opens things up a bit to chase electrical issues.

[Wheezyryder]

Alabrew- I did check fuse #7. I had already replaced all the fuses with new from prior electrical troubleshooting, but during thus can troubleshooting I rechecked the fuse and tested it for continuity. The over temp light definitely works, as it comes on reliably when I let the bike idle to long. And I have spent quite a bit of time visually inspecting the wiring. I'm using a flashlight to make things easier to see. So far haven't found any broken or pinched wires.

The voltage at the fan connector with key on and 15 and A2 jumped was .3 millivolts, so basically nothing

I checked for voltage at connector 15 with the key on. I got 12.35 volts. I then checked the battery at the terminals with the key on and got 12.5 volts so a little bit of voltage drop there. For reference, I turned the key off and the battery reads 12.72 volts.

[Laitch]

If these test connections are being performed correctly—that isn't a given—and you're getting these results with the adequate battery output voltage you've indicated, the temp switching relay or its connecting wiring is likely to be at fault.

[Wheezyryder]

Laitch- although I tried to follow the diagnostic instructions closely, it is definitely possibly that I'm somehow making some kind of mistake with the testing. Electrical things definitely aren't my strong suit.
I have a friend who's an electrical engineer and enthusiast of the R series Airhead BMWs. He is much more capable with electrical things than I am. Maybe I'll ask if he can come over and run through the diagnostics to make sure I'm not screwing it up somehow.

[Wheezyryder]

In the days before Covid, I would have already asked him to come over and take a look. These days, and given that I'm in a high exposure occupation, it might take some special arrangements to get it done.

[Wheezyryder]

Laitch- Turns out you were correct...It is definitely not a given that I would perform the test procedures correctly....And indeed I did not.

Due to my puzzling results, I invited a friend over to help me run through the testing procedure again to see if I'd screwed anything up. This friend grew up working in his father's auto repair shop, so it's no surprise that he's a better mechanic than I am. He quickly discovered a key mistake I'd made. I had misinterpreted the position of the various relay terminals on the temp sensing relay connector (E,9,A2, 15 etc). I was looking at the layout on the relay itself and failed to correctly interpret the position of the various leads. Once that became clear, the test results started to make more sense. We were able to get the over temp light to come on at the dash which I was not able to do before. We also discovered that there was no power coming to relay terminal 9 which should get power from fuse 6 according to the guide. We found that while the fuse itself was intact, there was no power coming to  that fuse terminal.

After scratching our heads for a little while, he suggested we call his dad who is an ASE certified master auto mechanic, owned his own shop for 40 years and now teaches auto mechanics at a community college. I was somewhat skeptical about his ability to diagnose the problem over the phone, but I was soon proven wrong. By asking questions, instructing us to perform various tests, and instructing us to trace the path of wires form the wiring diagram in my Clymer manual, he soon figured out that the power to fuse 6 comes from the fuel injection relay. He instructed us on how to put 12V to the signal wire to trigger that relay, which could be heard clicking. But still no power to fuse 6 with the fuel injection relay activated. I questioned whether the bike would run if the fuel injection relay were faulty. He said that a dipole relay can fail on just one circuit and still function on the other. To prove it we jumped 12V from the battery to fuse 6 while also jumping 12V leads 15 and A2 and the fan did come on. So he thought that a new fuel injection relay should power fuse 6, in turn powering the temp sensing relay and causing my cooling fan to work when it should. So I've ordered a fuel injection relay from Euro Motoelectrics and we shall soon see if the diagnosis is correct.

I was completely amazed at his ability to work through the problem over the phone. I could barely wrap my head around his thought process and I was looking at the bike and diagram in person. He is not a motorcycle guy, and was not aware that BMW made any motorcycles other than opposed twins. He most certainly is not familiar with the specifics of a K Bike electrical system. I was humbled to say the least.

[Laitch]

He is not a motorcycle guy, and was not aware that BMW made any motorcycles other than opposed twins. He most certainly is not familiar with the specifics of a K Bike electrical system. I was humbled to say the least.

He's a certified auto mechanic. The Brick is one of BMW's Peugeot auto engines mounted sideways—that's it. The electronic fuel injection system is similar to those found in thousands of old Subarus and other autos. That's how he tracked it to the injection relay. He wasn't in unfamiliar territory at all. He's a skilled orderly thinker with automotive experience. Skill comes with orderly thinking, clear observation and patience; otherwise, having an expendable cash surplus is the way to go. 

[Laitch]

Of course, it's too early to start celebrating. Please update us when you install the relay and the radiator. 

[daveson]

But the fuel pump also gets power from fuse 6, unless the wiring behind the fuse has been altered?

Jumping 15 and A2 should turn the fan on, even with no power to fuse 6, because 15, green/black wires, are supplied by fuse 7.

[Wheezyryder]

Laitch- agreed I'm not celebrating just yet. Still plenty of opportunity for failure here.

[Wheezyryder]

Well it looks like it was the fuel injection relay. Got the part in the mail, plugged it in, reassembled the bike and took it for a test drive. Rode a few miles to get it warmed up then pulled into a gas station and let it idle. Sure enough the fan came on, and the temp light did not come on. Thanks to everyone for their input and advice.

Now on to other problems:
Right side blinkers don't work
Headlight is extremely dim
Tachometer doesn't work even after I got the speedo working
Hard starting especially when cold

I will say I've really enjoyed working on this bike. Can't wait to put some miles on it

[Laitch]

Thanks for the update, Wheezy.