93 K75S - Coolant Fluid Expansion Tank

[GasStation]

I was told to keep the expansion tank coolant level on the low side (⅓ up the filler tube). This would help with the overflow. However, I find that when I run the bike hard (+5000 rpm range) I end up with some coolant stains on my righthand leg pants and splash back all over the righthand luggage and expansion tank. I check the rubber nipple cover or cap and it is perfect without any damage.

Anyone else with this condition?

[Scott_]

Any chance you have a crack/leak in the rubber hose between the expansion tank and the connection at the radiator?
Or even a crack in the expansion tank itself

[GasStation]

I will check, however, the liquid appears to come straight out of the cover nipple. I purchased a new rubber cover despite the condition of the older one being adequate without apparent damage.

The overspray pattern appears to be originating from the top of the expansion tank, leaks down the tank and falls prey to the wind stream as it smears everything downwind.

The former owner told me he kept the coolant level very low in the expansion tank as raising it to the BMW standard only caused more mess outside the tank; was curious to know if anyone else had that issue or came to that conclusion.

[mystic red]

Just don't add any more and keep an eye on the level. It will find it's own level. Then watch it to make sure it doesn't keep going down. I keep my K11 at the fill level to keep from getting sprayed.

[Motorhobo]

Is that the bottle with the plastic sight glass? That plastic deteriorates, gets brittle and starts to crumble. My original one turned to crap and the used one I got off fleabay was nearly as bad. I ended up ordering a new one from the dealer. Is it possible it's not coming from the top at all but is leaking from the transparent plastic level indicator? That might have the same spray pattern as if it were coming from the top ... Some spray might even get on the top as well. Plus, if the leak is anywhere along the indicator it would leak even if it were only half full due to all the liquid sloshing around. Maybe try some silicone sealant around the edge of the plastic sight piece?

[GasStation]

Thanks Motorhobo,

It could certainly be the expansion tank and so I will keep a close eye on it for leaks. The next time I run the bike and there is a leak, I will post some pics and then you guys will be able to see what I see.