On our workshop day I took along a spare temperature sensor. It turns out that I inadvertently took the wrong sensor. I took what I believe is a sensor for the 16v engine. I have looked online trying to find the test values for the 16v sensor but I've had no luck. Can anybody point me in the right direction?
Regards Martin.

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.

Laitch thanks I've already done that and the readings are totally different to the 8v hence the query. It is the brand new one that was sent to me as an 8v one, but the only way you can get reading it to probe both pins there is no connection to the sensor body. I was going to give it to somebody with a 16v but it looks like it's either a trophy or a bin job.
Regards Martin.

Martin, I recall reading that all the K bike engine temperature sensors have the same specs on the temperature/resistance curve.  2500 ohms at 20C and 190 ohms at 100C.

Wish I knew where to find it for you.  Did some looking this morning, but no joy.

The sensors are different because the Motronic does the switching for the fan where in the Jetronic it was done with the temperature relay.  From what I can see in the electrical schematics, the 4 valve temperature sensor does not read between the pins and the shell, but between the pins.  Since the Motronic is doing the fan switching the sensor only needs one output signal.

Hope this helps.

Is it possible that it is part #62162325348 for the temperature gauge on a 16V bike? This is separate from the engine temperature sensor.

https://www.realoem.com/bmw/enUS/showparts?id=0533-USA-07-1991-89V1-BMW-K_100_RS_0523,0533_&diagId=62_0535

This shows as a single pin hook up so like not the culprit.

It's now relegated to being a fishing sinker.
Regards Martin.

MartinW wrote:It's now relegated to being a fishing sinker.

It'd make a nice pendant, especially if you keep it polished.

It's yours Laitch, I'll give it a buff and put it to one side, next time your in the neighborhood drop in. I'll even shout you a Beefy's pie and a éclair.
Regards Martin.

I'll make plans for visit a week before next Valentine's Day.

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.

Ok, new bike to you.  Coolant isn't critical anymore, almost all long life coolants work with the aluminum of the brick engine as long as they are mixed with 60% DISTILLED water.

My first 16Valve K100RS would overheat anytime I rode it in temperatures above 80F.  After flushing the cooling system(twice) and removing the radiator and soaking it in white vinegar overnight the bike ran without overheating in temps over 90F.

Besides removing a large quantity of dead bugs from the radiator fins, the vinegar scoured out the remaining mineral deposits from the radiator passages.  It appeared that a previous owner must have been running the bike on well water.

DadofHedgehog wrote: it's likely the temperature sensor ---

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.

You should remove the thermostat to see if it opens at the correct temperature—starts at 85ºC, fully open at 105ºC. Do that carefully so the gasket around its perimeter isn't damaged. There are no replacements.

The temp warning light wasn't triggered and the fan wasn't triggered. If the cap created the correct pressure then you'd verify the coolant temperature sensor operates correctly and verify that the warning bulb in the instrument cluster lights. What type of cap did you install? The coolant temperature sensor is just behind the radiator right side as you face the front of the engine. It interacts with the Motronic to activate the fan. I don't recognize the term temperature valve.

Point-Seven-five wrote:
My first 16Valve K100RS would overheat anytime I rode it in temperatures above 80F.  After flushing the cooling system(twice) and removing the radiator and soaking it in white vinegar overnight the bike ran without overheating in temps over 90F.

Besides removing a large quantity of dead bugs from the radiator fins, the vinegar scoured out the remaining mineral deposits from the radiator passages.

Yeah, I agree this is likely a good-to-do task that will help. Thanks!

Laitch wrote:

DadofHedgehog wrote: it's likely the temperature sensor ---

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.

I don't recognize the term temperature valve.

"Temperature valve" is also known as a "thermostat" in Latinate English ;-)

[quote="DadofHedgehog"][quote="Laitch"]

DadofHedgehog wrote:
"Temperature valve" is also known as a "thermostat" in Latinate English ;-)

Quaint! When in Rome . . .. Of course, we aren't in Rome.

Getting back to .75's radiator cleaning; I flush gravel road tailings from my moto every fall.