Hello everyone,

I'm new to the forum and to the K100. I have a K100 RS which unfortunately had to go in for a headgasket replacement soon after buying her. The mechanic (Daniel), with over 30 years working on post-war to modern BMW, told me the radiator cap was defective and the temperature sensor wasn't too healthy either. So after replacing all the parts the bike was handed back last Saturday.

My worry is that in urban traffic she seems to run very hot, and the the fan only comes on when almost in the red zone. Disturbed by this, I returned to the mechanic's yesterday and he informed me that his K100RT behaves in exactly the same way. On the highway there are no worries as there's enough airflow through the radiator. Daniel also recommended against fitting a manual switch for the fan.

My questions are:
Whether it is possible to fit a temperature sensor switch which will turn the fan on earlier?
Does anyone get false readings from their guages as the temp guage needle sometines wildly oscilates and fuel sudenly goes to zero with half a tank or less, even with a full tank it reads 3 quarters.
If a indicator LED could be fitted to light up when the fan is runningas I can't hear it when I have my crash helment on?
Does anyone else's K behave in the same way?

Many thanks in advance, besides these little idiosyncracies, the bike is fantastic....German engineering, quirky but solid. What makes matters worse is I thought I'd be used to these odd habits after having classic and youngtimer Mercedes-Benz for the last 7 and a bit years!

Thanks again, Martin

HI Martin

Whether it is possible to fit a temperature sensor switch which will turn the fan on earlier?

If its an NTC type where the resistance drops with temp
I reckon a low value high wattage resistor fitted in parrallel could
bias it so the fan gets switched earlier
10 ohm 5W for instance perhaps?
Some experimentation would be needed to know for sure of course
An override switch may be an easier quicker option initially but manual switching obviously depends on your
observation and input


Does anyone get false readings from their guages as the temp guage needle sometines wildly oscilates and fuel sudenly goes to zero with half a tank or less, even with a full tank it reads 3 quarters.

I find my gauges are pretty steady and reliable luckily
If I had your problems the first thing I'd do is open check and clean all related connectors
and see if that helped

If a indicator LED could be fitted to light up when the fan is runningas I can't hear it when I have my crash helment on?

I'm sure it could, thought about doing one for myself but but would have to look at the wiring diagrams to refresh my memory on how its configured
It could probably be done with just an led, a resistor, some wire and appropriate connections in the right places


Does anyone else's K behave in the same way?
Nope but I guess i'm just lucky

Thanks, I'll have a look at the connections for the gauges. it may be a poor connection.

The temp sensor is something which does worry me more so I shall investigate and cross reference with the mechanic, I would imagine the auto-electrician I use should be able to help with the LED indicator, I just wanted to check the idea out on this forum where you all seem to know your bikes well.

Just had a quick look at the wiring diagram before I go out
It looks like the fan has a permanent ground and switched supply
on a purple/yellow wire.
If I have it right then an override switch could apply power to the P/Y wire
on demand and an indicator led would be attached to the p/y wire and ground
leds are polarity senstive of course (anode to live cathode to ground)
and a std led will need a series resistor.
I often use 1K's on bikes cars etc cos I got lots of em and this drives em just fine

A small bulb connected between the p/y and ground will work just as well of course

Martin K100RS wrote: Whether it is possible to fit a temperature sensor switch which will turn the fan on earlier?

Reg_k100rs solution to fit a high wattage resistor in parallel to get the fan switching ON earlier would work, BUT.....
The fan starts when the engine runs at 103 degrees Celsius. The temperature warning light glows at 112 degrees Celsius. I you modify the value of the resistance on the sensor to start your fan earlier, you will also modify the signal for the temp warning light. Both fan and light receive their signal from the same sensor and are controlled internally by the temperature switching unit . This is why IMO this solution is not good.

Martin K100RS wrote:If a indicator LED could be fitted to light up when the fan is running

I do have an LED for the fan on my bike. It is simply mounted in parallel with the 2 wires of the fan.
The only inconvenient of this system is that on my bike, when cruising over 4,500rpm, the LED is slightly glowing. I have 2 plausible explanations for this:
a) with the wind pressure, the fan is turning on its own and acts as a generator
b) A positive voltage is backfeeding to the fan circuit. (same issue as the charging light slightly glowing)

This slight glow is just an inconvenience as the LED is very bright when the fan is on.

Both fan and light receive their signal from the same sensor

Ahh!
Oh well, just whip the bulb out then !


jus kiddin

Its true of course that 'tweaking' the sender will affect the
temp unit so the fan and warning light get triggered earlier.

But it could also be argued that if the fan comes on earlier it may never get to the point where
the red light has to be switched.
Horses for courses of course and Im just playing with ideas
if you modify any part of a system you should run tests, make observations and consider
the effects rather then
jump in wildy.

( not that it ever stopped me setting fire to stuff )

My fan comes on at midway up the gauge not near the red
I wonder why Martins comes on so late in comparison?

I also wonder what the argument Daniel has against a manual override for the fan?
I'm doing an electric fan project for the CX and will have a manual override.
I figure if all else fails, I can switch it manually
I can also use it for occaisonal checks to see its working.
Mine runs so seldom I'n concerned it will get the weather and seize again

Fan Status led glowing
With Berts experience in mind
If I fitted one I might try running the led from say a 620-100 voltage divider
this may soak away any stray voltage withut affecting the supply to the fan.
Maybe, I could probably live with it glowing dimly too

Reg,

Daniel is against fitting a manual switch as he argues that if the fan is running and a signal is sent to the 'brain' it could cause some sort of problem. I had a manual switch fitted to the GoldWing I had some years ago however, that bike had carbs and points.

I'm very open to ideas as I do intend to run this bike on not leave it gathering dust like its 3 previous owners did! Brazil in summer has very high ambient temperatures and the last thing i want is the bike cooking its own engine.

I've briefly read this thread and the manual switch seems does seem viable. I do need to go back and study it some more though, I'm no electrical whizz!

http://k100rt.aforumfree.com/electrical-f8/oh-dear-and-now-temp-issues-k100-rs-t829.htm

Has anyone actually fitted one?

BTW, does anyone know where can I find an EPC for the K100?

Use an adjustable thermal fan switch to make the radiator fan kick in sooner. They're easy to install. Below is a picture of the Flex-a-lite adjustable thermal fan switch.

It adjusts between 180°F and 240°F. There is a manual configuration and automatic configuration. In the automatic configuration, power can be supplied to the fan even with the engine off to cool the bike right after it is turned off.
The switch is available from Summit Racing and other after-market vendors.
http://www.summitracing.com/parts/FLX-31147/

Martin K100RS wrote:Daniel is against fitting a manual switch as he argues that if the fan is running and a signal is sent to the 'brain' it could cause some sort of problem.

I don't want to put down your mechanics as it is nice to have somebody thinking about the implication of a modification. However, he's wrong and he may not know that the water temperature sensor is in fact a dual sensor. (It is pretty difficult to get our kind of expertise of the K100 for somebody working on all BMW models.)
One side of the sensor is sending a signal to the EFI computer and the other side is sending a signal to the temperature switching unit. They are 2 different circuits and the modification of one circuit doesn't affect the other.
To resume, it is safe to install an override switch.

Bert

Hi Martin,
There are two issues here one is the gauge indication and that is as you say worth checking the connections are all good. Bear in mind the fluctuating fuel gauge can be just a bad connection at the plug between the fuel tank and the bike frame. T

he other issue is your concern that the bike is running hot. I strongly urge you to find someone with an infra red temperature sensor and pop over to them and measure the temperature of the radiator and the engine heads (not the exhaust pipes in the field of view when you measure) that will tell you if you have a problem.

The thermostat opens at 83 from memory (someone correct me if I am wrong) and I have know people agonise over "overheating" when in fact it is not. Our bikes leak a lot of hot air into the area around the rider and there are a number of things one can do to reduce that. That often gives riders the impression the bike is overheating it is so hot whereas it is just the heat shed by the rad.

So my advice before jumping in and doing fan mods is see what the temperature actually is and report back. We are here to help.
Regards,
K-BIKE

The thermostat opens at 83 from memory (someone correct me if I am wrong) ...

85

So my advice before jumping in and doing fan mods is see what the temperature actually is and report back. We are here to help.

Check that the fan is turning freely. The rotation spec for the fan is 4200rpm.

Regards,
K-BIKE [/quote]

Many thanks to everyone for all this advice.

The info about the manual switch will be passed on to Daniel ASAP.

The bike runs at half way up the gauge on the motorway, the temp rises only when in slow or urban traffic. As the fan is electric I do understand that this is little air flowing through the radiator until the fan kicks in, and there lies my main worry especially as summer is coming and it does get pretty hot around here then. The manual switch is more for 'peace of mind' than use every day.

I shall look into the connections this weekend. I hope that a simple clean up will bring everything back into harmony.

Crazy Frog wrote:

Martin K100RS wrote:Daniel is against fitting a manual switch as he argues that if the fan is running and a signal is sent to the 'brain' it could cause some sort of problem.

I don't want to put down your mechanics as it is nice to have somebody thinking about the implication of a modification. However, he's wrong and he may not know that the water temperature sensor is in fact a dual sensor. (It is pretty difficult to get our kind of expertise of the K100 for somebody working on all BMW models.)
One side of the sensor is sending a signal to the EFI computer and the other side is sending a signal to the temperature switching unit. They are 2 different circuits and the modification of one circuit doesn't affect the other.
To resume, it is safe to install an override switch.

Bert

Bert, Just to check...the over ride switch is wired just as shown on this very forum isn't it?

The override switch should be wired between pin #15 and pin #A2 of the temperature switching unit.

Do remember leaving it running at idle will run the battery flat if it is a bit weak as the bike does not charge. Check the temperature before you fit the fan switch because as long as it is cycling on and off and keeping the temperature under control then do not worry about what the other bike temperature gauge says they are not very accurate.
Regards,
K-BIKE

K-BIKE wrote:Do remember leaving it running at idle will run the battery flat if it is a bit weak as the bike does not charge. Check the temperature before you fit the fan switch because as long as it is cycling on and off and keeping the temperature under control then do not worry about what the other bike temperature gauge says they are not very accurate.
Regards,
K-BIKE

The battery is new so no issues there. The fan does cut in and out. As I have mentioned earlier the override is more of a 'peace of mind' issue than anything else.

I'm now a shade confused because the schematic posted on this thread appears to be slightly different to the one on the other thread. Which one is correct or are they both correct?[url=

The difference between both schematics is that this one will turn a light ON when you have the switch activated to bypass the temperature switching unit.

Crazy Frog wrote:The difference between both schematics is that this one will turn the temperature warning light ON when you have the switch activated to bypass the temperature switching unit.

Excuse my ignorance, but is that a good idea?

In fact, with this one, you even don't have to put the extra bulb. The temperature warning bulb will glow as soon as you bypass the temp sensor.

Crazy Frog wrote:In fact, with this one, you even don't have to put the extra bulb. The temperature warning bulb will glow as soon as you bypass the temp sensor.

As I have mentioned before, Daniel - the mechanic, is wary if doing this kind of mod. Surely this is a very safe and really easy way to put in a manual switch without too much fiddling about or even the risk of damaging the bike's 'brain'.

Hi Martin!
I`ve got an original BMW temp gauge on my -88 K100RS.
My fan will not come on until the needle is hitting the red area.
This is usually happening while riding in very slow traffic in hot conditions.
When the fan is engaged the needle will come down to about 3/4 of the scale.
Then rises again to next to the red line and comes down again.
I think this is pretty normal.
I`ve been riding in very hot conditions and never had a problem with overheating.
The switch is interesting and the knowledge of this forum is superb.
Cheers,Wikur

I have a switch fitted spliced in the sensor wire at the temperature relays and connect it to ground with a switch in the crashpad. When I switch it, the fan comes on and it shows the red light in the speedo as the relay actions as if the bike is overheating. No problems at all with the bike in any other way so I don't understand why your mechanic thinks its such an issue. Ask him for the reason and let us know. Alternatively, make him a member here and let him post??

wikur wrote:My fan will not come on until the needle is hitting the red area.

The red zone (when the temp warning light starts to glow) is 111º (Celsius). The fan is set to start a 103º (Celsius). Only 8º difference!
I don't know at what temperature the fan should stop spinning, but I assume that it should be around 85º. (The thermostat opens at 85º (or maybe 83) and this must be the optimal temperature for the engine.)
If the temp unit was shutting off the fan at 100º, the fan would go ON/OFF every 2 seconds when riding in hot condition.

If you check at the following graph, the resistance of the water temp sensor is very minimal between 82 and 100º. These 8º temp difference may be reflected by an angular displacement of the needle of approximately 10º.
It must be scary to watch the needle if you don't know how the water sensor reacts to a raise of temperature.
By the way, I don't have a temp gauge on my bike and this is pure speculation according to temperature and resistance of the sensor.

I may be wrong but somebody having a gauge could spend time to record the position of the needle according to the resistance of the sensor. It would this worry at rest.

wikur wrote:Hi Martin!
I`ve got an original BMW temp gauge on my -88 K100RS.
My fan will not come on until the needle is hitting the red area.
This is usually happening while riding in very slow traffic in hot conditions.
When the fan is engaged the needle will come down to about 3/4 of the scale.
Then rises again to next to the red line and comes down again.
I think this is pretty normal.
I`ve been riding in very hot conditions and never had a problem with overheating.
The switch is interesting and the knowledge of this forum is superb.
Cheers,Wikur

Thanks, Wikur That's exactly what happens with my bike. Thank you again for your input.

My personal feeling is modifications like this should be done temporarily to fix a problem, as it seems you don't actually have a problem at the moment you are introducing a modification to fix a non problem. Please don't take that as criticism, I am thinking your bike is working well so why modify it. I am speaking as someone who accidentally bumped the kill switch when stalling a bike at the light wearing big heavy mittens and could not understand why it would not start much to the anger of the vehicles behind me :-) I have not done this modification but I strongly suspect that with the switch on and the fan running you will not be able to re-start your engine if you ever stall it until you switch off the switch which is a potential for another non start issue when you are flustered after a stall say in heavy traffic at the light change. The non start feature is designed into the bike for safety reasons to allow the bike to run when overheated but once you stop the engine it will not allow a re-start until the engine has cooled. The BMW bike alarm used that feature to deter theft. Anyway if you decide to put it on we will all be interested to read how it went.
Regards,
K-BIKE

K-Bike,

I understand your concerns and agree with you. Let's see how it goes with the bike, as I am getting used to her and her little habits. After all, she is 22 years old!


Crazy Frog,

Out of curiosity, the terminal where the aux. switch would be fitted is in the relay box under the tank, isn't it?

Martin K100RS wrote:Out of curiosity, the terminal where the aux. switch would be fitted is in the relay box under the tank, isn't it?

Yes it is.

Regarding K-Bike's comment; it depends. The ECU reacts on a shortened temp sensor wire as if the bike is seriously overheated and will allow it to continue to run, but as soon as it is switched off, for whatever reason, it will not allow a restart. But here the difference between the Jetronic and the Motronic bikes become important. Bikes with the Jetronic brain have actually two temperature sensors in one housing, where one works for the ECU and the other for the temp relais, which switches the fan and the warning lights. On these bikes there is no issue with such a switch set-up. Off course with the single sensor Motronic the effect of shortening the sensor wire will affect the ECU and K-Bike's advise applicable.

Does anyone have a simple step by step explanation of how to wire in the aux. fan switch? I'm no electrical whizz and , obviously, it's no good giving the electrician an explanation in English as he doesn't speak it! So I will need to translate the steps he needs to take.

many thanks, Martin

P.S.: I'm familiar with the expression "Don't fix it until it's broken". However, after just having spent a small fortune having the head gasket, radiator cap and water temp. sensor replaced, I prefer the "prevention is better than cure' philosophy.

Martin K100RS wrote:Does anyone have a simple step by step explanation of how to wire in the aux. fan switch?

Check out this posting:

http://autos.groups.yahoo.com/group/kbmw/message/38394

It has a description and accompanying pictures for your electrician friend.

Thanks Robert, I've just signed up for another web group!