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I have a Rotax 912 ULS in an SLSA. that had the 5 year rubber done. Starting after 5 or so flights, the engine developed slight leaks beginning at the radiator outlet, and then, at each of the hose clamps leading to the reservoir ( four in all), along the route that involves the metal pipe running along side the left side of the engine. Each leak was independent of the other. The leaks were minor seepage and not more than 6-8 ounces of coolant mixture was lost the the total of all the leaks.

To remedy the leaks (per my mechanic's agreement),prior to each flight thereafter, I tightened the respective hose clamp a 1/4 turn or up to the resistance torque of the clamp screw. Again each instance was independent of the others. I have done about 12 flights since the rubber replacement.

The first leak at the radiator outlet has stopped and the second leak at the reservoir inlet also stopped, but the other two persist though at lower rates of seepage. I plan to continue carefully torquing the remaining troublesome hose clamps as long as I don't encounter dead torque resistance.

All other connections are dry.

One more piece of information. The plane is hangared in central Florida. Temp range right after the service were 85/60F and have currently dropped to 65/45F. I was told this could exacerbate the problem

Is this normal experience? When I purchased the aircraft last year with 600 hours, there were no leaks. Granted I conservative on adding torque to the hose clamps. As a Lycoming/Continental convert, I'm just trying the learn what is considered normal.
  • Re: Post 5 year hose replacement coolant leaks

    by » 5 years ago


    Try using the Rotax spring clamp Part# 851 645 it holds constant pressure regardless of temps. If your new to Rotax sign up and take the line maintenance course. It will pay for itself many times over.

    https://lockwood.aero/parts/four-stroke-parts/912-s-914/rotax-912-s-914-water-circuit-expansion-tank.html

  • Re: Post 5 year hose replacement coolant leaks

    by » 5 years ago


    When using clamps on these outlets place the clamp up, but not on top of the flared end of the fitting. The spring clamp or screw clamp will apply more pressure to help stop any tiny leak when the clamp is up close to the flared end of the pipe. I have seen this many times and just move the clamp closer to the flare and it has always stopped the leakage.
    Try it and let us know.

    p.s.
    After placement of a new hose and a screw clamp these should be checked for tightness after 25 hours.

    p.s.s.
    Don't over tighten fuel and oil hose clamps. You may cut the interior of the hose. So no Godzilla force.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


  • Re: Post 5 year hose replacement coolant leaks

    by » 5 years ago


    Adjusted the hoses. Moving the clamp worked. Three out of four issues stopped. One connection seeps maybe a drop per flight. No drops on the lower cowling, just a tiny wetness at the junction with a brief odor of coolant when I check for leaks after a flight.. I guess I can live with that. Is it too naive to have absolutely no seepage?

  • Re: Post 5 year hose replacement coolant leaks

    by » 5 years ago


    You should see NO leakage. Make sure the leakage is from under the hose and not from the fitting itself. Put that clamp up close to the flared end under the hose, but not on top of it. If that doesn't work try rotating the clamp 90 degrees. If that doesn't work use a Wurth Zebra wormdrive clamp. These are a raised rib type clamp and not the garden hose variety serrated holes one. Much more solid clamp.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell


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