Hi,

Since fitting the RT fairing, I've been plauged with heat problems. When I ran the motorcycle in its RS guise, the bike would heat up but the radiator cooling fan managed the heat admirably. The temperature would be brought down and the fan would cycle properly.

With the RT, heat builds up a great deal more and a great deal faster. I am aware of the heat issues with the RT series but this problem is more I believe. The temperature can be maintained if I keep the bike at speed. If I encounter stop-and-go traffic, the bike overheats. The cooling fan will engage when the temperature rises enough to trigger the fan relay. But the fan cannot seem to cool the fluid and eventually the overheat light comes on. I have to turn off the bike to prevent damage to the engine. I would expect that the fan would provide enough air flow to maintain or lower the temperatures...but it doesn't. Even after getting past stop-and-go traffic, the temperature takes a very, very long time to lower.

The fan is brand new. The fan circuit functions normally and correctly. I have changed the cooling fluid twice this year. I use 50/50 mix of water and BMW anti-freeze recommended by BMW for this engine (aluminum block). I have kept the radiator area meticuliosly clean so there is no air flow blockage. I don't have any Kguards or reflective material to redirect or trap heat.

So given all this state of affairs, the only thing I can think of that might be problematic is the thermostat. It is the original thermostat from when I bought the bike. Should I replace it as a matter of course?

Another thing is a radiator flush. I've never done one and don't believe one has been done ever. Will this flushing help to remove scale that may be inhibiting thermal transfer? If so, how do I do a rad flush (I have no idea)?

Thanks for any other suggestions that you may have to help my heat problems.

Cheers,

Hi there, This is what I would do, in order
Check the air flow path to be shure there are no obstructions up and down stream the radiator.
Check the radiator cap gaskets, if worn or deformed the cap wont hold the pressure and the fluid will go to the overflow vessel instead of staying in the sistem cooling the engine. and wen the engine gets cold the air will leak into the radiator not alowing the vacuum to recover fluid from the vessel
Check de Thermostat. There is a cheking procedure on the Haynes, to be shure it fully opens at the stamped temp, if faulty replace it, but do not remove the thermostat as a solution.
During summer change the coolant mix to 30/70 (pure water is better working fluid but needs the anti corrosive aditives)
Check the pump impeler. If worn you´ll have not enough flow to cool the system
Flush the radiator, with aluminium compatible product (procedure is in the can), and if possible take it to an specialist for full cleaning.
Let us know.
Best regards
JAP

Rob
Not sure why your getting these problems
Mines an RS with RT fairing but didnt have any issues

One thing I did have even withe RS fairing was I found (eventually)
the pipe from the rad cap to the expansion bottle was
perished and allowed coolant to escape
not a lot but it did make the bike run hotter and the fan came on a lot.
So I guess its worth checking coolant level and you have no leaks

I'm currently running with no lowers
I removed them for engine servicing and havent bothered to refit them yet
we get a lot of heat off these motors and I figured I'd leave em off for the summer

When riding in town during hot weather, my fan starts quite often, but the temperature light never glow.
You may have a problem with the water temperature sensor or the temperature monitoring unit. It would be interesting to know what is the real temperature of the engine when the fan starts. Could you borrow an infrared thermometer or have a mechanics checking it? Just let the bike running on the center stand and check it.
Flushing the radiator may not be a bad idea, but checking the thermostat may not be a bad one too.
The RT fairing retains more heat than the RS, but it should not be a problem as both bikes have the exact same cooling system.

Bert

Guys,

Thanks for the valuable feedback.

JAP:
I'll check the radiator cap. I believe it was ok at the last refill but I see how a faulty cap can cause problems. There are no objects hindering the flow of air through the radiator so that can't be the problem. The water pump will have to wait until I've tried other easier fixes, like the thernostat.

Reg:
The line from the rad fill pipe to the overflow tank is brand new so that is not a contributor to the problem.

Bert:
If you recall, I posted a short synopsis of the various temperatures versus the temp sensor resistance measurements for calibrating the water temperature gauge. You moved that thread to the tutorials. My water temp gauge is showing that the fan comes on at the indicated mark on the gauge which leads me to believe that the temperature sensor, temperature monitoring unit and electrical wiring inbetween is OK. However, the sensor for the temp gauge is different htan the one for the Jetronic so there might be some creadance in that observation. I have an IR thermometer and can perform some checks.

It could be just that with the additional fairings you have put more strain on a cooling system that was close to its limit due to age etc.

As for the radiator flush it is usually just a case of running water back through the radiator in the reverse direction to flow until it runs clear. Much more relative in the good old cast iron engines.

I wonder if anyone has had a new core in the radiator as it is not uncommon in cars.

And reg_K100RS Or should that be RT ) how is the heat situation without the lower fairing as I came to the conclusion also that it might be the best option for summer.

The best solution that I saw on the RT was somebody with a spare set of lowers. He had cut the majority of the side making big openings to have the hot air escaping. He left the back of the lowers intact keeping the protection for the legs. The bike didn't look bad at all.

Maybe I can take a page from the "Best PC Case Designs" book. Computer cases have exhaust fans that promote the circulation of hot air out of the case. Maybe mounting small 120mm 12V fans on the lower vents will exhaust the hot engine air quicker, promoting more air exchanges per minute than possible with convection venting. Hmm.....

Sounds like a plan as at speed there is probably a venturi effect but at lower speeds heat just builds up under the tank and can not be very efficient as both the fuel and airbox would heat up which is not ideal under any circumstance.

That is the "problem" with the RS/RT BM's they are designed to run at speed all day every day.

Hi,

I had a similar problem. At speed say 80km/h there was never any problems, but in slow traffic, the fan would come on and the light would follow in short time.

The solution: the fan speed was way too low. The spec for the fan speed is 4200rpm and mine was running at approx 1500 (dirty bearings).
With a new unit the fan comes on frequently, as it should, but no more red lights.

Phil
I've actually been sweating riding a K in the summer so leaving the lowers off seemed worth a try and its definitely helping.
Reduced 'sauna effect' in traffic riding and at speed theres no
major drawback as far as I can tell unless its peeing down with rain and my tootsies get wet or wetter than they would with a full fairing.

One snag I did have was at first I sometimes knocked my knee against the sharpish edge of the upper ( oh! ya bugger !!) but learnt to keep away from it after a while by adjusting my riding position.
I know it looks a bit odd without them but havent felt any real need to put them back on so far.
I also used cable ties on the bottom to keep the rad guard secure
Just took a pic of it

Unless you need 50% antifreeze I suggest you drop the percentage of antifreeze down to the amount you need for your climate and where you park your bike. Then add some Water Wetter from Redline. Last but not least make absolutely certain that the rad is free of bugs, spider webs, dust, seeds and grasses as quite small amounts affect the ability of the rad to shed heat to the air. Don't water blast from the front to the back, that will get water in the fan motor and damage it.
Regards,
K-BIKE

K-BIKE wrote:Unless you need 50% antifreeze I suggest you drop the percentage of antifreeze down to the amount you need for your climate and where you park your bike. Then add some Water Wetter from Redline. Last but not least make absolutely certain that the rad is free of bugs, spider webs, dust, seeds and grasses as quite small amounts affect the ability of the rad to shed heat to the air. Don't water blast from the front to the back, that will get water in the fan motor and damage it.
Regards,
K-BIKE

Thanks K-bike.

I have watered down the concentration of anti-freeze to maybe 40% now because water is the primary heat conductor. I don't want to go much lower than that because winter storage in Canada can mean that the temperature will drop to -17 C or lower at times. I'd rather not risk a frozen rad with risk of burst pipes.

As I mentioned in the original post, I've made sure that the air pathways are very clean and free from blockage. I haven't blasted the bike with water to wash it so I haven't threatened the fan condition.

UPDATE: I was out riding today. The stifling humidity has lifted here and the temperature was 15C in the morning, rising to 23 C. The cooler ambient temperatures were kinder to the bike and it ran fairly well and cool, even in stop and go traffic. I'm going to test the thermostat and replace it if the old one shows signs of fatigue. But I'm going to ride out the season and tackle the heat issues when I put the bike away for the winter.

Thanks to all for the sage advice. This is a great site; so many knowledgeable people with desire to help.

I once had a similar problem on a Ford Escort ( a long long time ago!!) and the issue was that the water pump impellor had become seperated from it's shaft. It therefore was no longer turning with the pump.

Hi Rob! I never had a problem with the bike overheating with that fairing, even though there was a lot of heat buildup during stop and go traffic. I wondered if BMW has a different thermostat for the RT or RS ? hope you find the solution!! b

Hi,

I'm still suffering from overheating problems in stop and go traffic. I prepped today for a system flush and thermostat replacement. While doing so, found that the overflow bottle was completely empty. I know I filled it to just below maximum when I refilled the system not long ago. So where did all the fluid go? Which also begs my silly question ... did the cooling system suck the overflow liquid back into the system because there was air trapped in the system? This is all I can think of since I don't have any tell tale signs of fluid under the bike. If so, I feel silly since I thought I got out all the trapped air. If there was trapped air, then the coolant vol;ume was lower than it should have been.

yes, it got sucked back into the radiator and it is not your fault. You will always have some air in the system when you do a fresh fill. The idea of the overflow is to catch the coolant expanding under heat and pressure and then when the whole thing cools it gets sucked back in.
With no leaks you will reach the point where no air is in the system and the coolant level in the overflow will go up and down with temperature (and pressure).

It is possible that you have a leak on one of the hoses or connections, but as the bottle gets empty I guess that the leak is pressure (hot) related.

I guess that you should keep filling both the radiator and the bottle. I think after a few goes you will deduce what is going on. Keep checking all the connectors for signs of fluid or residue due to coolant additives.

I am a bit puzzled by your problems. Cooling depends on coolant flow (pump) and air flow (fan). The construction of the engine helps because it is aluminium (good conductor). So, unless you have a leak (lack of coolant) I suspect that one of the two (fan or pump) are at fault.
I assume here that blown head gasket is not a problem? Yes? If so the compression test will tell you that.

Ned wrote:I am a bit puzzled by your problems. Cooling depends on coolant flow (pump) and air flow (fan). The construction of the engine helps because it is aluminium (good conductor). So, unless you have a leak (lack of coolant) I suspect that one of the two (fan or pump) are at fault.
I assume here that blown head gasket is not a problem? Yes? If so the compression test will tell you that.

Ooo, don't want to go there just yet!!!


I'm working through a list of potential fixes with "dismantle water pump" and "check head gasket" as the last items.

Another question. Which direction should the fan blow air? Towards the front wheel, sucking air from the engine compartment? Or towards the back of the bike, sucking air from the front of the motorcycle? I can't find an answer to this question on any forum, funny enough. I just want to make sure that my "factory-fresh" fan is wired properly.

TIA.

P.S. Finished the flush and, using pure water, bike on the center stand, engine running at 1500RPM, the fan cycles on and off just fine. The temperature according to the water temp gauge drops as what I was used to when the motorsysle was in RS guise. It might have been confined RT fairing, slightly low coolant volume and wrong antifreeze ratio that was my problem. I'm going to (1) install an 82C thermostat, (2) drop the EG ratio to 4:1, (3) run without lowers for a while and (4) monitor the overflow tank level like a hawk. Canadian Tire is getting Engine Ice so I may switch to that for the summer months.

Fan: mine blows from front to back and because it is rated at 4200rpm it should be noisy and obvious. It should pull "cold" air through the radiator.

Compression: up to you, but it should be a 30min job. Remove the plugs, ground plugs to the engine, test each cylinder by cranking 5 times per cylinder. 5 times is my method. After 3 or so revolution the pressure should be close to max. Also, I sit on the bike, press the gauge by hand onto the plug hole and crank.
Another way to check if you have exhaust leak into the cooling system is to look for bubbles in the coolant at the engine runs (cap off) and smell the coolant. The smell of exhaust should be obvious.

Temperature: As your fan cycles, that almost certainly eliminates temp sensor (provided the temp is correct).

coolant concentration: well the best of all coolants is plain water, but because of corrosion and freezing point of water you must use the correct ratio of, in Canada, antifreeze. In Sydney we talk about coolants and boiling points.

EG ratio?

Ned wrote:Fan: mine blows from front to back and because it is rated at 4200rpm it should be noisy and obvious. It should pull "cold" air through the radiator.

S**T. Mine's blowing in the opposite direction to yours. This must have been the problem all along. That means nice warm engine compartment air is being forced through the radiator, not allowing the coolant to reduce in temperature. I'll investigate the fan conections first thing. Thanks Ned!

EG = Ethylene Glycol. Antifreeze. I picked up this acronym from another forum. Guess I got carried away.

No problems. Happy to have been able to help.
However, I would keep to your suggested testing protocols just to make sure all is good.
On my bike, one thing that I did was to replace the short run of black tubing between the radiator cap and the overflow tank with a clear type so that I can see the the coolant move around at a glance. I guess that it amuses me more than it helps

I tore into the motorcycle's cooling systems again yesterday. Removed the radiator and swapped the positions of the contacts in the fan motor connector. Reassembled the bits and pieces and ran several tests. This time, hot air is blowing out of the vents in the lowers and the fan actually cools the bike just as before. I took the bike out for a shale-down ride, stopping often to see if the fan cycled. It did. I could not reproduce my elevating heat symptoms described at the beginning of this thread so I am declaring the problem solved.

Thanks to all K-bike gurus for your help. I am improving my mechanical abilities with this bike with each repair.

Ahhhhhh !
So thats what it was.
Glad you've resolved it.
How did the connections get reversed Rob ?
Assembly error?
can the plug be inadvertently connected the wrong way around?

reg_K100RS wrote:How did the connections get reversed Rob ?
Assembly error?
can the plug be inadvertently connected the wrong way around?

Ok, I admit it! You pulled it out of me! Assembly error.
When I installed the new fan back in the beginning of the year, the blade sliced through the wire within a couple of days. I repaired the wire but apparently got the contacts reversed. I never associated this fix with my heating problem until I asked the question about air flow above. Next time, I'll take photos before disassembly.

The plug is polarized so it cannot be inadvertently reversed.

Never mind Rob
yer sorted, thats the main thing
I bet between us we could quickly fill a new section on things we
shall we say
'Could have done better'

We may start a new post about the worst mistake that we made on our K bikes. I personally broke a brand new dust cover on the clutch push rod (The one on the back of the gear box were you have the adjusting screw).
I always tell everybody to maintain the push rod lever but I was on the rush and didn't do it.

robmack wrote:Maybe I can take a page from the "Best PC Case Designs" book. Computer cases have exhaust fans that promote the circulation of hot air out of the case. Maybe mounting small 120mm 12V fans on the lower vents will exhaust the hot engine air quicker, promoting more air exchanges per minute than possible with convection venting. Hmm.....

I was thinking the very same thing on my way to work this morning. I am reluctant to alter the thermal switch thingy or hack the wiring loom about. This simple idea could be wired straight from the aux PTO and a simple switch and fuse, thus not interferring with the original wiring.