collant liquid loss K75c 1986

[colmedo]

Hi,

purchased a 1986 k75c just months ago. Made some basic hands on (oil, filter, etc) and started riding but found out that at some point coolant liquid starts coming off site where I understan thermostat is sitting. This is strange and don´t hear the radiator fan turning on. Can of course tighten those screws but don´t know torque so as to ensure doesn´t brake (have appropriate tool to measure torque)

Guy who sold me the bike mentioned he realied on this space to have accurate guidance and comments. So purchased thermostat and its gasket and temp sensor but before trying to see if changing parts fix this wanted to ask if anyone experienced similar conditions or any hint, comment or guidance. Read on this space there is a relay somewhere bellow sit that is the one that  turns fan on and off. Will see if can test on that relay if fan is working (also ideas or comments are highly appreciated)

Never changed such parts (as mentioned new to this bike) but will try to see if haynes manual give hints on how to perform this. If any specifics please let me know your comments.

[sooprvylyn]

This is the thermostat cover.  The part you probably have to replace is the rubber o-ring on the cover itself.  See the top image below.


The thermostat has a rubber gasket as well(bottom picture).  This often deteriorates over time.  Might as well replace the thermostat and gasket since you got it and will have the cover off anyway.  You will almost certainly need the o-ring for the cover to stop the leak.



Fan issues are sorta common on these bikes.  Turn your fan to see if it spins.  If no, you may need to replace the motor or the fan entirely.  You  can also disconnect the fan wire and connect the pins in there directly to the battery to see if it spins with power. 

The cooling system on these bikes is pretty darn good.  If you are riding on cooler days, your fan may not come on.  I can usually ride in like 65 degree weather without my fan ever coming on.  Almost always when the fans have a real problem it is the motor is seized.  This is because the cooling system is pretty good and the fans often dont run, so the motors get seized from disuse and grime.  Its not that likely the issue is with the relay.

If you have a bad fan motor, come back and we can tell you your solution options.

[colmedo]

Thanks for your help!!

[Laitch]

The torque value for the thermostat cover screws is 3±0.45 Nm. Go to this link and download the BMW K75/K100 2V workshop manual from the list. The torque value came from its Radiator section. I can see that the thermostat cover is bent slightly. Tightening its bolts won't help. You need to determine why it's bent. From records on this site, this leak started in 2023. An aftermarket thermostat was used as a replacement. Perhaps its height is too great so its top hits the cover and keeps it from tightening fully.

The fan should start after the engine idles for 15–20 minutes. In Montevideo's climate, it shouldn't operate frequently this time of year with high temperatures in the low 70ºF unless you are riding in slow moving or stop-and-go traffic. In such traffic on warm days, it should cycle on and off every few minutes. Verify that the fan blades can be rotated easily when the fan is shut off. Has the temperature warning light turned on?

Check the thermostat cover fit, check to see if the fan blades move easily, and see if the fan starts during the time frame suggested previously. Report back. Beware coolant has a sweet taste and can be fatal to dogs and cats that consume it where it has spilled. It is also deadly to humans and other creatures that somehow ingest it.

[colmedo]

got it! So its a long history of such problem. Will take deeper look into it anc come back. Maybe need to purchase new lid.

By the way I mysef did purchase original parts (thermostat, oring) from motorrad but never imagined such cover or lid was the problem.

Thanks!