K11 Owners Group

poetryandmotorbikes · Mad Brick Rider Joined: 17 Sep 2009 Posts: 80

Eesh. This bike seems to have come with its fair set of problems. Not disgruntled, but a little disillusioned. At least the engine is good (despite its popping and the occasional back fire -- that's good right?).

So the hot weather is in, and I am riding 200 or so KM a day for kicks, because I am a career student and too poor to do anything but drink coffee and ride motorcycles. It is not so bad.

Because of the hot weather, the bike seems to be overheating. When I ride at night, it's fine. During the winter, the aux fan would occasionally come on if I left it idling while my heated grips warmed up. Now that the weather is in the 20s (degrees) during the day, the fan comes on in traffic and just recently the temp idiot light has been coming on. Driving home today it took next to nothing for it turn on and the light followed only after about a minute of idling in traffic.

Where is the best place to start? Tomorrow morning I am going to take out the thermostat and test it, I will probably follow that with a coolant change. I've heard that if the fans have gone that the horn doesn't work. Horn works and I hear the fan everytime it turns on. Fresh oil, fresh oil filter.

Anyway, where to start?
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1992 K75S

Motopoeta | Beautiful Vintage Motorcycles Daily

Ted · Posted: Thu May 13, 2010 7:31 pm Post subject:

My guesses...

1. Radiator Cap - if it is faulty and the system cannot properly pressurize you will overheat quick. My K11 had this problem, solved it with a new $15 or so cap. Not sure how to test it, but you can give it a good visual look over.

2. Radiator obstructions/bad fan. Check to make sure the radiator isn't munged up with dead bugs, and that the fan is actually turning and blowing air when the fan motor runs - I have heard more than one fan blade coming loose from the motor.

3. Coolant - degrades over time so it must be changed every other year. Leaving it in for way too long can cause scale build-up in the system. Personally I recommend folks spend the extra $10 and get the BMW purple stuff, and use only distilled water. You will need a gallon of coolant, gallon of distilled water (40/60 ratio), and a copper crush washer for the drain plug. You might also consider replacing the coolant reservoir sight tube as they degrade over time, as well as carefully check your hoses.

4. Temp sensor?

5. Two wild cards from the IBMWR K-Tech pages: clogged fuel filter causing impeded fuel flow and hence hotter fuel, and a cracked crankcase breather hose causing a lean condition and its accompanying elevated heat.
_________________

Ted

KOG#1

Flying Duck · Posted: Thu May 13, 2010 7:33 pm Post subject:

Backfire is normal when engine braking.

Stat and coolant change is where I'd start to look if the fan is working normally.
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

Ted · Posted: Thu May 13, 2010 7:38 pm Post subject:

Ahh yes the backfiring Smile

You can minimize that by properly adjusting your throttle shut-off switch.
_________________

Ted

KOG#1

Flying Duck · Posted: Thu May 13, 2010 7:47 pm Post subject:

Ted:

Don't the radiator caps start spitting up when they go bad?
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

Ted · Posted: Thu May 13, 2010 7:49 pm Post subject:

Mine showed signs of spitting when I got the cap off but I never noticed it until then.
_________________

Ted

KOG#1

poetryandmotorbikes · Mad Brick Rider Joined: 17 Sep 2009 Posts: 80

BMW dealer wants $80 for a new thermostat. Any restrictions on thermostats? Can I use one from another K-Brick? A 1995?
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1992 K75S

Motopoeta | Beautiful Vintage Motorcycles Daily

Ted · Posted: Fri May 14, 2010 3:50 pm Post subject:

Looks like the thermostat (17111460716) is constant across all K75, K100 and K1100, as is the cap (17111464720). For what it is worth, the thermostat is only $46 at Max BMW, and probably another $5 or so cheaper at Chicago BMW if you call to order. The radiator cap is only $15.
_________________

Ted

KOG#1

rydor · Posted: Fri May 14, 2010 11:24 pm Post subject:

DO replace the rad cap! (right Ted Laughing

)

hfxrzw · Mad Brick Rider Joined: 30 Jan 2009 Posts: 78

RE backfiring - adjust the TPS. They should not backfire, the TPS is fitted to prevent it (it switches injection of above 2000 rpm when the throttle is closed).
Re overheating - It is very rare to have a K75 overheat. Normally the fanmotor is burned out as it is stuck for lack of use. Have a good look at the hose coming from the radiator cap to the reservoir. When they perish every time the bike warms up you will loose coolingwater and when it cools down you will pull air in the radiator, which reduces the cooling capability. You can get your radiator cap tested at a dealer if one is nearby, otherwise on an old bike its a worthwhile investment. Test your thermostat I don't think they go often.
I had a similar problem on my 1984 K100RT which was resolved (eventually!) by replacing the coolingwater temperature sensor. This was faulty although giving the right resistance at 20C. If you (or a mate) have a temp gun you can see if the actual temperature is indeed so hot or if it is just the switch gear that indicates so. That will direct your further search.
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Cheers, Rene

Greetings from Florida.

BMW K100 '85

beemeerr11 · Flying Brick Rider Joined: 05 Mar 2006 Posts: 168

RobWheatley · Posted: Mon May 17, 2010 3:17 pm Post subject:

Tim (Midland Section) · Posted: Mon May 17, 2010 7:32 pm Post subject:

Flying Duck · Posted: Mon May 17, 2010 10:26 pm Post subject:

It's caused by overfueling in moderate to hard engine braking when you chop the throttle. You can get them to backfire even with a properly adjusted TPS if you chop the throttle quickly enough.

If you don't engine brake, no backfire.
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE