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Thread: 1985 K100RS coolant boiling over?

  1. #16
    Quote Originally Posted by mcmlcccvrs View Post
    I can't really run the bike until it is hot with the cap off as after a very brief period the coolant rises in the filler neck and will come out the top long before the coolant is even warm.
    That tells me that indeed there is air trapped somewhere which expands more at a lower temperature than the coolant liquid does.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  2. #17
    Dances With Sheep GREGFEELER's Avatar
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    From what I gather your problem is coolant leaking from the cap area, indicating a problem with either the cap, or the filler neck. Perhaps there is a crack in the filler neck that only opens up under heat and pressure, so perhaps you might consider replacing that part? On the MaxBMW parts fiche (below) it looks like the filler neck is #24, part number 17 11 1 460 313, which they list as costing $7.82. That seems like a low price for such a part, so you should verify.

    Parts link: https://shop.maxbmw.com/fiche/Diagra...2&rnd=07242017
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    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  3. #18
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    Hello,

    In your post #12 you indicate that you replaced the center gasket. If you are talking about the smaller inner gasket (#26 on the parts diagram,) that gasket does not seal the cap to the atmosphere. I believe that gasket seals the pressure relief valve (inside the cap) to the coolant filler neck. If that gasket was leaking it would allow pressure to escape from the cooling system to the expansion tank before the cooling system reaches the design operating pressure, but not escape to the atmosphere. If you have fluid escaping from around the cap to the atmosphere, I believe that means it's the larger outer gasket that is not sealing properly.

    Regards,

    Richard Flood
    Commerce, Township, MI

  4. #19
    3 Red Bricks
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    Richard is correct. Coolant coming out at the cap indicates that the OUTER cap gasket is not sealing.

    In your middle picture, it shows a nick in the outer sealing surface of the filler neck between 10 and 11 o'clock. That would cause a leak of coolant along the threads as the bike heats up. It would also suck air into the radiator as it cools down. Do yourself a favor and follow Greg's suggestion and buy a new filler neck. It will probably solve all your coolant problems. The cap has to have a good seal at BOTH the inner and outer gaskets.

    Make SURE that there are no cracks in the hose from the filler neck to the expansion tank!




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  5. #20
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by 98lee View Post
    {SNIP}...In your middle picture, it shows a nick in the outer sealing surface of the filler neck between 10 and 11 o'clock. That would cause a leak of coolant along the threads as the bike heats up. It would also suck air into the radiator as it cools down...{SNIP}

    Bingo! Good catch, Lee. That certainly could be it.
    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  6. #21
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    "Richard is correct." Thank you 98lee, I don't get that often.

    Regards,

    Richard Flood
    Commerce Township, MI

  7. #22
    Dances With Sheep GREGFEELER's Avatar
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    Quote Originally Posted by richo2006 View Post
    "Richard is correct." Thank you 98lee, I don't get that often.

    Regards,

    Richard Flood
    Commerce Township, MI
    Clearly a limitation of the other people in your conversations.
    Greg Feeler
    Ambassador & amateur K-Bike collector, it seems
    1972 R75/5, 1990 K75, 1990 K1, 1992 K75S, 2003 K1200RS

  8. #23
    Quote Originally Posted by 98lee View Post
    Richard is correct. Coolant coming out at the cap indicates that the OUTER cap gasket is not sealing.

    In your middle picture, it shows a nick in the outer sealing surface of the filler neck between 10 and 11 o'clock. That would cause a leak of coolant along the threads as the bike heats up. It would also suck air into the radiator as it cools down. Do yourself a favor and follow Greg's suggestion and buy a new filler neck. It will probably solve all your coolant problems. The cap has to have a good seal at BOTH the inner and outer gaskets.

    Make SURE that there are no cracks in the hose from the filler neck to the expansion tank!




    Hi Lee,

    That nick that you believe you are seeing is an illusion created by the ring of dried coolant around the sealing surface of the filler neck. When wiped off there is nothing there. I can see no issues with the filler neck whatsoever, and I did inspect them a few weeks ago as posted farther back in this thread. All new Samco coolant hoses (just because) and new hose from filler neck to expansion tank too.

    Cheers,
    Tom

  9. #24
    So I had some time this morning and decided to squeeze hoses again. Nothing to lose, right? Put the bike on the side stand and continually squeezed the hose that runs across the top of the engine block. It still bubbled up air and some large ones that spit coolant out the top, and the coolant level, while visible, was down in the upper hose. I also squeezed the lower hose, but in using both hands I could not look into the filler neck. I went back and forth between the two. Guys, can these systems really be this difficult to remove trapped air? I took my time filling it.

    I put the bike on the center stand and started it up. The coolant rose up in the filler neck to the point where I had to shut the bike off or it would have spilled over. This shouldn't happen. If I have understood the procedure for these bikes after replacing coolant, I should be able to run the bike with the cap off to watch for trapped air being released. As Paul mentioned, and it was a thought I had, this indicates trapped air being heated, expanding and raising the coolant level.

    Tom

  10. #25
    Quote Originally Posted by mcmlcccvrs View Post
    So I had some time this morning and decided to squeeze hoses again. Nothing to lose, right? Put the bike on the side stand and continually squeezed the hose that runs across the top of the engine block. It still bubbled up air and some large ones that spit coolant out the top, and the coolant level, while visible, was down in the upper hose. I also squeezed the lower hose, but in using both hands I could not look into the filler neck. I went back and forth between the two. Guys, can these systems really be this difficult to remove trapped air? I took my time filling it.

    I put the bike on the center stand and started it up. The coolant rose up in the filler neck to the point where I had to shut the bike off or it would have spilled over. This shouldn't happen. If I have understood the procedure for these bikes after replacing coolant, I should be able to run the bike with the cap off to watch for trapped air being released. As Paul mentioned, and it was a thought I had, this indicates trapped air being heated, expanding and raising the coolant level.

    Tom
    1. Obtain a good turkey baster syringe and a two quart pan.
    2. Start bike.
    3. As coolant rises in filler neck use baster to draw out coolant and squirt it into the pan.
    4. When all of a sudden you get a big burp of air clean up the mess.
    5. Slowly refill the system while the engine is running.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  11. #26
    Quote Originally Posted by PGlaves View Post
    1. Obtain a good turkey baster syringe and a two quart pan.
    2. Start bike.
    3. As coolant rises in filler neck use baster to draw out coolant and squirt it into the pan.
    4. When all of a sudden you get a big burp of air clean up the mess.
    5. Slowly refill the system while the engine is running.

    I think you're right, Paul. My current, repeated approach is not yielding different results. A project for Thursday morning.

    Tom

  12. #27
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    There is no way that coolant will come out around the cap threads IF the outer gasket of the cap is sealing. Any expansion of the coolant will go into the exansion tank (hence the name). If the outer gasket leaks, it will also suck air into the radiator when the coolant cools.

    Fix the leak and you will probably fix the rest of the problems. There are only three components involved with a leak at the cap; the cap, the outer gasket, and the filler neck. Your problem is with one (or more) of those.

    Actually, another possibility; if the hose to the expansion tank is plugged and the hose is loose or cracked at the cap end, it could blow coolant toward the cap threads making it look like it is coming from the threads.




    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  13. #28
    Okay, so here is where I am at everyone. Fired up the bike on Thursday morning. As it was warming up, I had to extract 180ml of coolant with my BMW turkey baster so it wouldn't come out the filler neck - not much, really. I did see some bubbles. I let the cooling fan cycle a couple of times and then shut it off as I had no more time.

    I left the bike until Friday morning and poured all of the 180ml back in. After pouring it in, the coolant level was visible in the upper hose at the horizontal point before it transitions to the vertical towards the filler neck. Fired the bike up and let it warm up. I had to extract 110ml so it wouldn't overflow the filler neck and saw some more bubbles. Let the cooling fan cycle a couple of times with no issues. I shut the bike off and left it until this morning.

    I poured the 110 ml back in and started up the bike. I had to extract 80ml as the coolant was rising in the filler neck. Saw some more bubbles. Really? Still? What I did see today - and not that it didn't happen on Thursday or Friday as I could have missed it - was the coolant level immediately dropping as soon as the cooling fan switched on. Thermostat opening? If so, isn't that a little late? Clymer states thermostat opens at 85C and cooling fan comes on at 103C.

    I am going to let the bike cool down for a few hours and then start it back up again without adding the 80ml of coolant I extracted and see what happens.

    Thoughts, suggestions, guys?

  14. #29
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    I'm getting the feeling (I could be wrong) that you aren't understanding how an expansion tank coolant system works.

    When cold, the radiator is completely full, the hose between the cap and the expansion tank is full, and the expansion tank is at least to the low mark.

    As the coolant heats up and expands, the pressure cap (inner gasket) opens and allows the excess coolant to go through the hose to the expansion tank keeping the radiator full. When the coolant cools in the radiator and contracts, it creats a suction that sucks coolant back into the radiator thereby maintaining a full radiator. All of this is dependent on the outer radiator cap seal maintaining a closed system.

    With the cap off, like you are doing, you are sucking off the expansion with your turkey baster and sucking in air when it cools. Then you are topping it back up and trapping air in the radiator. That doesn't show anything. If you look at the expansion tank, the distance between the hot and cold line is about equal to the amount of coolant that you are removing and replacing.

    Get the outer cap gasket to seal properly.




    Last edited by 98lee; 05-24-2020 at 01:54 AM.
    LONG MAY YOUR BRICK FLY!

    Ride Safe, Ride Far, Ride Often

    Lee Fulton Forum Moderator
    3 Marakesh Red K75Ss
    Mine, Hers, Spare

  15. #30
    Lee,

    All fair comment considering. As I upgraded the filler neck cap to the new style, which had new rubber seals obviously, then I have no choice but to replace the outer rubber seal or revert to the original cap altogether. There aren't ten different ways to hand tighten the cap.

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