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Coolant Leak

Category: 912iS Technical Questions 5 months ago

Plane/Engine (Rotax 912is) is 1.5 years old, 130 hours.  This winter, I noticed coolant drops on the front wheel pant directly underneath the engine. Naturally, I checked the reservoir and there was no loss of liquid.  I asked some knowledgeable Rotax folks and they said "this happens sometimes with Rotax motors in the winter due to uneven expansion (metal vs rubber)."  Then one day I was taxiing to the runup area and my Dynon went crazy with warnings, I noted that the coolant temp was skryrocketing.  I shut the motor off and saw a bunch of coolant on the tarmac.  I pushed the plane into the hangar.  I found where the leak is coming from, where a rubber hose meets a metal pipe... see my finger in the pic.  I removed the temp-protective tape.  The clamp is a spring type clamp.  My Rotax mechanic suggested I put a worm clamp on and refill the reservoir.  I did that. started it up and no leaks.  On the morning of the day to fly to the shop, I noted drops on the wheel pant again.  But there was enough coolant.  After landing at the shop the mechanic told me that I didn't have the (newly added) worm clamp tight enough.  No leaks on the way back... 

The other day, I went to the hangar,  after a cold night, and once again... drops on the wheel pant.  Leaking from the same place.  Is there anything I can do other than 1) putting a 3rd clamp on ( in addition to the existing spring clamp + the new work clamp), 2) removing the hose and adding some sealant?, or, 3) wait out the 5 years rubber replacement and just accept the rubber/metal expansion/contraction imbalance.

Thank you... 

 

7860_1_coolant leak.jpg (You do not have access to download this file.)
  • Re: Coolant Leak

    by » 5 months ago


    If hoses leaked because of "Uneven Rubber to Metal Expansion" (???) then every connection in every engine would be leaking.

    What you have is a basic old-fashion Leak!

    Fluid leaks are notorious for leaking in one place and dripping at another.

    Your dual clamps are not stopping the leak because it is not leaking at the clamps.  You're barking up the wrong tree.

    In your photo, it looks like there is a tiny split in hose's outer jacket just to the right of the clamp; right where the hose bulges as it passes over the flared end of the tube.

    There could be another split on the backside that you can't see.

    Also, the clamp is wet, if it was leaking past the clamp and out the end of the hose, coolant would not be traveling uphill.

    Instead of removing the hose and adding some sealant;  try removing the hose and replacing it.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


    Thank you said by: Andrew Gibson, RotaxOwner Admin

  • Re: Coolant Leak

    by » 5 months ago


    Bill is right on. I had the number 2 cylinder coolant output hose to 80 degree fitting leaking. Tried new clamps, tried worm clamps, no luck. Finally ordered new hose, used the new factory clamps and all is well.


    Thank you said by: RotaxOwner Admin, Andrew Gibson

  • Re: Coolant Leak

    by » 5 months ago


    Bill Hertzel wrote:

    If hoses leaked because of "Uneven Rubber to Metal Expansion" (???) then every connection in every engine would be leaking.

    What you have is a basic old-fashion Leak!

    Fluid leaks are notorious for leaking in one place and dripping at another.

    Your dual clamps are not stopping the leak because it is not leaking at the clamps.  You're barking up the wrong tree.

    In your photo, it looks like there is a tiny split in hose's outer jacket just to the right of the clamp; right where the hose bulges as it passes over the flared end of the tube.

    There could be another split on the backside that you can't see.

    Also, the clamp is wet, if it was leaking past the clamp and out the end of the hose, coolant would not be traveling uphill.

    Instead of removing the hose and adding some sealant;  try removing the hose and replacing it.

    I also have this issue, in fact I've had to refill my coolant overflow tank twice this winter. I was told the same thing metal vs rubber and temperature differences... I'll try to investigate it a bit more!


  • Re: Coolant Leak

    by » 5 months ago


    Let's put this Metal vs Rubber Myth to bed...

    First, consider that this is no different from the 100 million Rubber Hoses in automobiles that are connected to the metal engine blocks that don't leak every winter.

    Then consider that the difference between the coefficient of expansion of Aluminum vs Rubber is 30 parts per million per degree F. (30ppm/°F)

    That would amount to 0.003" per inch per 100°F which reduces down to ~0.004" for a 200°F temperature change on our 3/4" hoses.

    Then, as the rubber expands and contracts more with temperature than the Aluminum, the colder it gets the tighter the rubber shrinks against the metal.

    And finally, "They" are asking us to believe that a 200°F Rubber hose is so stiff that it will not flex the thickness of a piece of common printer paper.


    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    Bill.Hertzel@Yahoo.com
    Clicking the "Thank You" is Always Appreciated.


  • Re: Coolant Leak

    by » 4 months ago


    Bill Hertzel wrote:

    Let's put this Metal vs Rubber Myth to bed...

    First, consider that this is no different from the 100 million Rubber Hoses in automobiles that are connected to the metal engine blocks that don't leak every winter.

    Then consider that the difference between the coefficient of expansion of Aluminum vs Rubber is 30 parts per million per degree F. (30ppm/°F)

    That would amount to 0.003" per inch per 100°F which reduces down to ~0.004" for a 200°F temperature change on our 3/4" hoses.

    Then, as the rubber expands and contracts more with temperature than the Aluminum, the colder it gets the tighter the rubber shrinks against the metal.

    And finally, "They" are asking us to believe that a 200°F Rubber hose is so stiff that it will not flex the thickness of a piece of common printer paper.

    Sounds like when the weather is nice and this virus dies down we should meet back up for a flight and you can take a peak and see if you can tell where this leak may be coming from. I took the cowlings all off the other day and cannot seem to find it. Also my lane checks are starting to run a bit rough and moving around 120rpm between checks. 


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