BMW K bikes (Bricks)

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1Back to top Go down    coolant leak on Wed Aug 23, 2017 9:13 pm


Silver member
Silver member
I have a leak at the hose from the filler, where it meets the radiator. I replaced this hose about 18mths ago, due to a groove from the tank, and to be honest, the clamp felt like it could have been tighter. I also noticed a residue around the overflow cap. Is there anything I should be looking for that would cause pressure in that area specifically? The filler cap seems to have some sort of gauze filter in it which is filthy, but I can't see how to get it apart, and is it worth boiling the thermostat to see if it opens?

Woody, 1993 K75s.


2Back to top Go down    Re: coolant leak on Thu Aug 24, 2017 12:18 am

RicK G

Check out the hose for damage and if it appears OK put it back and tighten the clamps well. If you need a hose there will be a few here.
Check out the filler cap under the tank to be sure it seals and keeps the pressure because they sometimes operate above 100°C and so will boil if the cap does not seal and with summer on the horizon, Charlie had heaps of trouble with a non sealing cap, led him a merry chase.

"Every normal man must be tempted, at times, to spit upon his hands, hoist the black flag, and begin slitting throats."  from Mencken's 1919 Prejudices

Bikes 1993 K1100 LT, 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki X 2 for now

3Back to top Go down    Re: coolant leak on Thu Aug 24, 2017 1:26 am


Life time member
Life time member
....and if the cap is not sealing then it could be dribbling down the side of the hose to the radiator, making it look like its leaking from the lower connection.
You can get a replacement washer for the radiator cap.

1988 K100RT     VIN No.  0094680
1989 K100RT     VIN No.  0097367 (naked)  
1996 K1100RS   VIN No.  0451808
     Fuel:  95 Octane
Engine Oil: Nulon Full Synthetic 15W50
Gear Box Oil:  Nulon Synthetic 75W90

4Back to top Go down    Re: coolant leak on Thu Aug 24, 2017 10:35 am


Life time member
Life time member
If your cooling system is running hot and has mineral deposits you might want to do a good flush and while you're at it, you might also want to clean out the fins of the radiator.  I had problems with my K100RS puking out coolant on hot days.  After I removed 25 years of bugs and dirt from the radiator and the minerals from the bad water the previous owner used the overheating and coolant loss stopped.

While I haven't done it on any of my bricks, it is possible to boil the thermostat in white vinegar to clean up the minerals.

1994 K75RT
1994 K75S
1992 K100RS

1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175

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