Overheat light on, fan not starting

[Mavebrick]

I believe it’s probably a K75T which is the C repurposed for touring in America. The sheepsking “hack” wasn’t too successful. It was a hot day in Houston and i kept getting the red engine temp light but it would go off when I am moving and come back on a for a while at every stop light or traffic light. Hoping I did not do engine damage. The engine seems to be overheating and i did not hear the fan kick on.

[Laitch]

The engine seems to be overheating and i did not hear the fan kick on.

That problem can be approached using the following methods.

The OEM fans deteriorate from neglect and from their innate construction weaknesses. That fan should be starting up before the overheat bulb lights up.
Poke a dowel at a fan blade and see it you can turn it. Mine seized and yours be also be seized. The wiring of those fans also can deteriorate. For the heat of Houston, the best thing you can do if the fan isn't working is to remove it right now and replace it with a 6.5 inch Spal puller fan. There are a few ways to mount them. One is by modifying the cowl around the fan so the Spal can be inserted within it. This is how to do that.  You'll note the Photobucket watermark on each photo at that link. That distraction sometimes arises when accounts are neglected or electrical glitches at Photobucket occur. Use this site's photo server. Another method of mounting the Spal involves making your own bracket. Find that method at this link. While the radiator is off, spray clean its fins with water.

Drain the the coolant and coolant reservoir and replace the coolant using the BMW method found on p. 17-13.0 in the BMW K75/K100 downloadable from this site. Then idle the engine for 15 minutes out in the sun. In Houston, the fan should start running.
If those tasks don't do the trick, remove the thermostat carefully so the gasket and o-ring aren't damaged, put it in a pot of water and bring the water to boil. The thermostat should be opening a 185ºF and continuing until fully open.

If none of the remedies or tests above cure the problem, the problem lies within the coolant temperature sensor behind the radiator, the temperature sensing relay, or the radiator itself is clogged, but the fan and coolant quality are the usual suspects.

[Mavebrick]

Thank you for the detailed reply, I will start by checking on the fan. Do you think drilling a hole in the thermostat, assuming it is working, can help the issue as a stop gap till fan issue is resolved (assuming fan is shot)?

[Laitch]

Do you think drilling a hole in the thermostat, assuming it is working, can help the issue as a stop gap till fan issue is resolved (assuming fan is shot)?

Heck no! You must have meant "assuming it is not working," because If the thermostat is working, the engine is getting the coolest water available—without the brisk motion a fan, or wind from the motorcycle moving along the road. Drilling one hole wouldn't do squat to help cooling and drilling the valve so it looks like a salt shaker would send metal bits around to create cooling tube clogs. Ruining a working thermostat should be avoided. Get cracking, check the fan and check in here. We ready to weep in consolation. Assumption just won't help at this stage.

[frankenduck]

As L points out, it is most likely a dead fan issue or possibly an issue with the thermo relay.

You did not damage the engine if that light came on. That light comes on at 232F and beyond that, just like a car, the radiator cap will blow coolant all over your right foot at 248F and you still have not damaged the engine.

More here:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/tempsensor/tempsensor.htm

[Laitch]

That light comes on at 232F and beyond that, just like a car, the radiator cap will blow coolant all over your right foot at 248F and you still have not damaged the engine.

Don't let loss of coolant and a scalded foot keep you from damaging your engine! Eventually an irate and sirloin- or taco-hungry commuter behind you during your steaming crawl along five lanes of Houston's finest concrete will put a round through it for good measure. If you carry a colorful pennant on a telescopic pole and extended it when you finally need to stop and cool down your no-pressure version of a pressurized coolant system, it could serve as the target.
 

[The Mighty Gryphon]

The cooling fins on your radiator have nearly 30 years worth of dirt and insect life restricting air flow. 

Check the fan and when doing the replacement with the Spal do a soak, inside and out, of the radiator in white vinegar for an hour or two followed by a good rinse. 

A complete system flush is also a good idea.  Who knows what kind of water was used in the system over the years.

[Laitch]

The cooling fins on your radiator have nearly 30 years worth of dirt and insect life restricting air flow. 

Save the rinse water! Exotic insects carrying gawdknowswhatall have been migrating northward from the EUM, Latin America and the Caribbean for decades. Inquire at UTHealth Houston if there's a researcher there that's interested in examining the contents. You might play a part in successfully stalling the development a disease vector, or in discovery of a viable source of cheap protein to ensure the future of personkind.

[sooprvylyn]

+1 for probably a crapped out fan.  Spal is a good replacement, and not too hard to obtain or install.

Its a good idea to confirm its the fan before you order the  spal.  You can easily see if the fan works by unplugging it and just jumping the 2 pins in the connector to your battery directly, doesnt really matter which pins you conect to which poles, the fan will spin either way, just might spin backwards.  If it doesnt spin, the fan is broke...and time to order a spal.  If it spins, its something wrong w your eng temp relay.

If its the fan, go ahead and drain the coolant, and remove the radiator.  While you have the radiator off, check that the oem fan hasnt drilled into the radiator. Not sure if this is common on k75, but its really common on k1100.  Might as well check everything so you ca order everything you need together.

This is a pretty easy repair, and if you have the new fan and mounting materials, and some electrical tools to swap the oem wire connector to the spal fan, its like a 1-2 hour job. Remember, the fan is a pulling fan, so its pulling air in from the front of the radiator.

[frankenduck]

Replace fan:
https://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/fans/fans.htm

[Mavebrick]

Thank you all! I’m going to have to get to this soon. Will let y’all know if it’s the fan or what I discover. If fan is working, can I just install a manual switch so I can turn it on as desired?

[Past-my-Prime]

Thank you all! I’m going to have to get to this soon. Will let y’all know if it’s the fan or what I discover. If fan is working, can I just install a manual switch so I can turn it on as desired?

Lots of people here have done just that.

[frankenduck]

I've put fan switches on several Ks in the past. I no longer do because I never see the need to use them. The factory fan mechanism works fine.

JM02.

[daveson]

If fan is working, can I just install a manual switch so I can turn it on as desired?

No, I think so not.

Your brick has a problem that wants to be fixed. Adding an option won't fix the problem. The fan is supposed to come on before the warning light comes on, that is, at a lower temperature. That then cools the engine down until the fan turns off, then the cycle repeats. Therefore the temperature light should really never come on, if all is well. The temperature light has only come on once with my brick, when I unplugged the spinning fan on a hot day, just to see if the light would come on shortly afterwards.

You want to find out why the fan isn't turning on before the temperature warning light comes on.

[sooprvylyn]

100% agree w finding out what's actually wrong.

You can install an override switch AFTER you learn the real problem and resolve it if you like. Many put fan override switches on Ks. I used to because i love in got live in hot places, but I've stopped because the bmw system works as it should.

[Mavebrick]

I tried to poke a long screwdriver at the fan and it is not moving and i see a dead spider in there with cobwebs etc i am sure that fan has been out of commission for a while.i am going to have to replace the fan and also test the thermostat and change out the coolant while i am at it from the looks of it.

[Mavebrick]

Are there any other options besides the spal fan? Any el cheapo radiator fans from autozone or something? Also do you need to remove the gas tank to get the radiator and fan off to replace fan or you don’t need to?

[Laitch]

Any el cheapo radiator fans from autozone or something? Also do you need to remove the gas tank to get the radiator and fan off to replace fan or you don’t need to?

An el cheapo fan is not what you want for that job. A 6.5" Spal puller fan is what will keep temperature reliably stable.

Remove the tank. You also need to remove the debris from the fins and core of the radiator with back-spray from a hose while it's off the bike. If you intend to remove and test the thermostat, remove it carefully so you don't damage the ring gasket around the perimeter of the flange.

[Mavebrick]

Thank you Laitch, appreciate it! I’ll get the spal fan. Do you have to drain the coolant to remove and swap out the thermostat?

[sooprvylyn]

Thank you Laitch, appreciate it! I’ll get the spal fan. Do you have to drain the coolant to remove and swap out the thermostat?

You'll need to drain it to remove the radiator to swap the fan anyway.

If you plan to replace the thermostat, might as well replace the rubber gasket too. Sometimes you can get them together.

[frankenduck]

Are there any other options besides the spal fan? Any el cheapo radiator fans from autozone or something? Also do you need to remove the gas tank to get the radiator and fan off to replace fan or you don’t need to?

Fans are not particularly sophisticated so you could probably get away with using a cheap fan but the Spal fan is a proven quality solution for Ks so it would save you a lot of searching as well as peace if mind since it's a good product.

[Mavebrick]

Finally got coolant drained and radiator off. I have several questions. The coolant was dirty and tried to “flush” it pouring water through a few times. The overflow still has the old gunky coolant in. Do i need to siphon that out? Does the overflow coolant ever get sucked back into the system?

Also i see a random hose to nowhere probably someone disconnected it in the past.
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For the heating issue do people reroute the fuel return away from back of radiator? Or do they use insulation? Would any autozone fuel line work for the fuel return line if i wanted to replace it?

For adding a manual switch how do i wire to the two wire existing wires connected to fan to have bothmanual and automatic fan switching? Where is the ground located?


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[Laitch]

Finally got coolant drained and radiator off. I have several questions. The coolant was dirty and tried to “flush” it pouring water through a few times. The overflow still has the old gunky coolant in. Do i need to siphon that out? Does the overflow coolant ever get sucked back into the system?

It's good that you're cleaning out that mess. Clean the overflow tank throughly. Here's an explanation of how the system operates. It's from the Haynes classic Brick manual.

[frankenduck]

[Kaos]

I am not the biggest brick fan fan.
On top of all the mentioned fixes problem solevers etc.
And finding gunk in your coolant you might also to do the following:

Remove the coolant pump cap from the front and also check the situation there.
Gunk tends to heap up there, it also allows for better drainage.
White wine vinegar is an absolute good option to use for rinsing, but mix it with demineralized water 250ml to 750ml
Check the fan for obstruction/resistance.
While the system is drained you can check the electrics by removing the temp sensor and heating it with a heat gun (watch your fingers) or by sticking it in boiling water.
De keep in mind that rinsing works best on a heated cycle so you must ride with it.

For illustration purposes:

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