Checking if the temperature switch on my '93 K 1100 RS - when the needle reach WHICH point at the temperature gauge / dial should the ventilator fan switch on? As it is a heavy heat wave going on in my part of Europe, this question IS important

The temperature gauge has its own temp sensor at the bottom of the oil/water pump and operates independently of the rest of the bike's electronics.

The Motronic (which controls the fan) uses a temp sensor that more closely determines the engine temperature. It is located at the front of the motor and measures coolant temperature right as the coolant exits the cylinder head.

And if you're worried about the engine, if it does start to overheat the overheat light will come on and if it gets even hotter than that then the radiator cap will blow before it gets warm enough to harm the engine. The cooling system pretty much works like that of a car.

Thank you for your answer - only I still don't know when normally (from experience of other owners) does the fan switch one? When the needle reaches the last line before red zone? Or one before?

My buddy who is an expert for bike elctrics was telling me how on K1200 it's normall that the fa starts after needle has already reached the red zone

The bike I own now for 3 months had not been too well maintained so I am still checking everything. I still don't KNOW for sure is the fan working as it should - or the temperature switches

There really is no "temperature switch."  The Motronic control unit monitors the engine temperature and controls the fan as well as how much fuel the engine gets, etc...  If your fan isn't coming on then the temperature warning light in the instrument cluster will illuminate.

If you want to hear the fan then start the bike and let it sit and idle until the fan comes on. If the warning light comes on but the fan doesn't then your fan isn't working as it should.

The red mark is when my fan comes on. The blue mark is where the temp sits on a normal day 30°C and at the green mark on days that are around 45°C
The fan comes on at 103°C and will cool till the temp goes down to below 100°C so in heavy traffic it will cycle quite often.

ffbikersa wrote:
My buddy who is an expert for bike elctrics was telling me how on K1200 it's normall that the fa starts after needle has already reached the red zone

This is technically incorrect. The fan should come on well before the red zone, about 3/4 of total needle travel. However, there are variances at play as the 1200 cooling system is barely adequate for the job, especially in built up traffic or very hot conditions. Experience as taught me a few things after 15 years and 165,000km's of K1200RS ownership. A major cause of rapid heat buildup is dirty radiators. Biannually I remove the two radiators and soak them before cleaning them by giving them a firm smack onto a flat surface. It is amazing the road crap that accumulates between the fins that is then deposited on the bench! After a good clean the motor will run noticeably cooler and the fans will take longer to engage.

One thing I found is that if you blow a fork seal the oil will get back into the radiator fins and that makes dust and dirt build up very quickly. I remove the radiator and give it a squirt with degreaser then hose it out. Amazing just how much brown stuff comes out.

In my case, my K1100rs fan turns on immediately after turning the key, even with the bike still off. What tests should I do to see if it is the sensor or Motronic?

What year is your K1100RS? How many miles/kms?

Did it just start doing this?

Any recent mods?

duck wrote:What year is your K1100RS? How many miles/kms? Did it just start doing this?
Any recent mods?

It's a cafe racer project. 1993

Mine it’s 1993 and no mods. It’s happened when i start it...

Did you replace anything?  If you changed the Motronic (cat vs. non-cat) or swap it the wrong chip then that will cause the fan to run like that.

Is the overheat light in the instrument cluster illuminated?  If so then it might be a chafed temp sensor wire that's grounding somehow.  That will make the Motronic think that the motor is really, really hot and turn the fan on.

What are the last 7 digits of the VIN?

brunoresendelopes wrote:Mine it’s 1993 and no mods. It’s happened when i start it...

brunoresendelopes wrote: I'm new owner of K100RS from '90, and cafe racer project is already started !

brunoresendelopes wrote:My k1100rs don’t have tube . . .

Do you have two motos and one is a cafe racer? Which one is the cafe racer and which one is having the starting problem?

brunoresendelopes wrote:In my case, my K1100rs fan turns on immediately after turning the key, even with the bike still off.  What tests should I do to see if it is the sensor or Motronic?

Highly likely its the relay is stuck/faulty. It's in the electrical box under the gas tank.

Another possibility is that a prior owner added a fan switch that you don't know about. I've made ABS switches that double as a fan switch.  The down position is a momentary switch for the ABS and the up position is a non-momentary switch to turn on the fan.

Look in the relay box.  If there's a non-factory wire tapped into blue/yellow wire to the fan relay then grounding that turns the fan on.

We saw this symptom on a k1 last week. Fan came on when ignition was turned on. Turned out that the Motronic connector was not seated correctly.

Ringfad wrote:Abbiamo visto questo sintomo su un k1 la scorsa settimana. La ventola si è accesa quando è stata inserita l'accensione. Si è scoperto che il connettore Motronic non era posizionato correttamente.

Hi, can you be more precise on what you mean by "Motronic connector was not correctly positioned" as my ECU also has the same problem.
Thank you

The connector to the Motronic needed to be removed and reconnected and the fan then stopped spinning when ignition was switched on.
 
However a few months later the Motronic completely failed on this k1 and had to be replaced.

Ringfad wrote:Il connettore del Motronic doveva essere rimosso e ricollegato e la ventola ha smesso di girare all'inserimento dell'accensione.
 
Tuttavia, pochi mesi dopo, il Motronic si è completamente guastato su questo k1 e ha dovuto essere sostituito.

... I understand that I will have to look for a new ECU. A greeting and thanks