Laitch wrote:The 16V engine has the same thermostat opening temperature as the 8V; the fan and temperature warning light trigger temperatures temperatures are within 3ºC of the 8V when comparing BMW's cooling specs of the two models. It's reasonable to believe then that the parameters of the coolant temperature sensors of the two should be the same.
Dropping it into some boiling water monitored with a thermometer and spending some quality self-isolation time watching the readout with pencil and notepad should tell the tale.
Funny this thread came up now... After getting my new (to me) 1991 K100RS4-Valver serviced very recently and discovering that what was in the radiator was non-BMW cooling fluid (different color etc), the bike began to heat up on the way home, in stop-&-go situations, really fast. Happened twice, both at night on major road construction choke points, immediately cooling off when I was able to pick up speed. Both times, the temp gauge needle crept into the red and then the red dash light lit up.
I read up on the issue a bit, changed the radiator cap for a new one (I mean, why not instead of messing with the old cap's screens and gaskets), and then took it around the neighborhood last night. Small streets, stop lights, visiting friends. The temp gauge needle crept up close to, but NOT into the red... and as I was parking at a grocery store one mile from home on the return leg, with no warning BLOOOEY! the overflow cap exploded and the steam etc etc etc. I cooled it off, put some water into the empty overflow tank and got home. This time, the red dash light had never come on.
My mechanic thinks that since we eliminated the radiator cap gasket as the culprit, and with zero dash light warning, it's likely the temperature sensor --- the very 16-valve sensor you write about Martin.
Of course (shudder...) it might be a failing Motronic instead... or the temperature valve on the other side of the radiator... or something else entirely. Oh, the joy of new/old pre-owned bikes ;-)
With the RS fairing it's actually much harder to hear whether/when/if the fan comes on, unlike on my K75T.
And yes my leg still feels the steam, just a bit haha.