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I have been chasing a coolant leak on my 914F3 engine.  The engine has had a recent 5-year hose replacement completed.  Flew for about 12 hours and a leak started...very slowly.  Initially I noticed a small "spray" of coolant in the neighborhood of the overflow bottle - the upper cowling wasn't particularly stained but the firewall and the electronics mounted there was sprayed with fluid. Initially there was always fluid in the overflow bottle - with either a hot or cold engine (cold, it was down about 1/4 of the way).  After a few more hours of flying, and continually adding fluid, the leak is now significant - there is never fluid in the overflow bottle, and I've constantly added fluid prior to each flight.  However it isn't flyable considering the leak rate now.  Found a few loose hose clamps, including one that was absolutely loose and free to rotate.  Flew again for about 45 mins and the leak seemed significantly better but not resolved.  Flew again for another 45 mins and the leak became major again.  Don't think the hoses or clamps are the problem.... is there a possibility the cap is bad on the expansion tank? Any other options work taking a quick look at?

  • Re: 914F3 coolant leak/sticking wastegate

    by » 10 months ago


    I've just had a similar issue but not quite as bad as yours. The root cause was a loose hose clamp. One option is to pressurise the coolant system to about 1 bar, just before the pressure relief cap opens. That should help you see where you have any leaks.


  • Re: 914F3 coolant leak/sticking wastegate

    by » 10 months ago


    Thanks Kevin….I will do that. 


  • Re: 914F3 coolant leak/sticking wastegate

    by » 10 months ago


    Hi Tony! I believe I have seen your motor glider up at KAWO. 

    Check the pressure at the expansion tank. I used an automotive radiator pressure tester with 1/4 hose attached right below the rad cap. 

    and you might want to buy a new radiator cap too. They are difficult to test unless you tee into the 1” line to the radiator. 

    My katana had a scratch on the expansion tank lip and few small leaks in the cooling system as well as a clogged radiator and rubber rad seal that was torn. The scratch on the tank lip was causing a very small leak. Ironically it was still cooling ok. (We were chasing an overheating problem which turned out to be the muffler)

    What sorts of oil temps and Cht are you seeing?

     

     


  • Re: 914F3 coolant leak/sticking wastegate

    by » 10 months ago


    About 6 years ago, so don't know if its still the case, I purchased a Ducati motorcycle radiator cap,  same part number and specifications, as Rotax, at about 1/4 the cost. (Edit: On reflection this may have been a BMW radiator cap)

    On hose clamps - Remember, when using push on hose connections,  the hose MUST have the correct ID to  for the spigot.

    If correct the hose will seal of its own accord.

    The hose clamp is primarily to there to provide security (hose pulling off) and should be located just a few millimetres behind the spigot barb/swelling.

    Use minimal clamping pressure, to achieve a secure hose, over clamping (to stop a leak) is almost always a recipe for hose failure.


  • Re: 914F3 coolant leak/sticking wastegate

    by » 10 months ago


    Nick/Sean:

    Thanks for the information and heads up - very helpful information.  I plan to test the system this week, and check every connection again...also, the expansion tank is configured with the older .9bar radiator cap; I have a new 1.2 bar cap that I plan to install.

    CHt's and Oil Temps have been great - right in the middle, or even a little low, especially during cruise...but max time per flight has only been about an hour.

    I'm also dealing with a sticking wastegate....it needs constant lubrication (pre-flight) to operate smoothly.  When I hear it "squeak" during the pre-flight servo motor cycle, I know it needs lubrication.  The turbo was just rebuilt so it seems something is amiss on the lubrication of that particular unit.


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