Coolant leak

Category: General Tech Discussion 8 months ago
I have a 2010 912 uls. It appears to have a coolant leak running around the left rear spark plug area. I looks like it might be coming from where the elbow goes into the head. The hose seems dry. is there a gasket in there ? Is there a special Allen wrench to check those bolts as a normal one does not fit under the intakes?
  • Re: Coolant leak

    by » 8 months ago


    Usually if it is coming from that area it is the clamp or leaking where the elbow screws into that flange with the 2 screws. If it is the clamp move it towards the flange on the end of the elbow under the hose. You can feel it with your fingers. DO NOT place the clamp on top of the flange, but just up close by it.

    The other common place for coolant at the elbows is the elbow where it threads into the flange. Dump a little coolant to just get the level just below the elbow area. Now take the flange with the elbow off. Take a magic marker and mark the flange and tube so you you put this back together you know where to clock the tube in reference to the flange. You will need to heat the elbow where it screws into the flange fairly hot to loosen the Loctite. Then just screw it out. Clean the threads up and apply some Loctite 648 green all the way around the threads and then screw it back in to your clocked marks. Then put the flange back on. Make sure the "O" ring is in place. You can put the hose back on, but I always let it sit a while before I add coolant to make sure the Loctite is dry.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-574-1080 Home (TRY HOME FIRST)
    520-349-7056 Cell

  • Re: Coolant leak

    by » 8 months ago


    I had this very same type of leakage recently on my 700 hour 912uls. It was not the hose clamp area that was leaking, it was the flange/elbow and I couldn't tell which. Unfortunately, to get that flange out, there is no magic allen wrench. You must take out the intake manifold bolts and then you can pull up the manifold (with the carb still attached) enough to get a regular allen wrench on the two flange bolts. With the flange off, the o-ring can be inspected. Mine was very flattened and was no longer a round x-section. I strongly believe I could have just replaced that o-ring and been good, but since I had the flange/elbow out I replaced the whole thing including o-ring. Reinstalled it and the leak was solved.

  • Re: Coolant leak

    by » 8 months ago


    Do I have to remove the intake to get at those bolts out That hold the flange around the elbow? I might not be using the correct terms for these parts. I found the parts diagram but no corresponding parts list?

  • Re: Coolant leak

    by » 8 months ago


    Mine is almost 700 hours also and that looks exactly like what it is doing. We are gonna put it down for annual soon so one more thing for the list. It doesn't leak much only a few drops.
    How about this one while I have you. if I look up under the engine block there is tiny hole where there is always a drop of oil. Is that a vent hole for the crank case?

  • Re: Coolant leak

    by » 8 months ago


    The little hole you are referring to might be the oil vent hole for the water pump bearing/seal. According to a ROTAX rep (Roger*), a small amount of leakage from this hole is not unusual.

    See #75-00-00, Page 12, Figure 75-10 at : https://www.rotax-owner.com/manuals/MMH_912-914_Series_ED1_R6.pdf

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    * https://www.rotax-owner.com/en/rotax-forum/3-4-stroke-technical-questions/7167-oil-leak-from-water-pump-912ul#21740

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