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This morning I found that the overflow coolant bottle on my 912ULS that I had filled to 400ml (half full) had only 100ml after five hours of flight. There are no signs of any leak anywhere, including after a full power run up on the ground. Any ideas of APOSSIBLE cause or trouble shooting ideas? I suspect the system may have put to much back to the overflow bottle and/or that there is something wrong with the pressure cap on the expansion tank. Only 400 hours on the engine
  • Re: Low Coolant Level

    by » 12 years ago


    The overflow bottle is not the concern. Uncap the cold engine and stick your finger in the resevoir. If its full, your safe, go fly.
    Watch the bottle, Mine fluctuates from half to empty depending on atmospheric pressure, phases of the moon and heat of the engine at inspection.

  • Re: Low Coolant Level

    by » 12 years ago


    Jospeh

    The coolant will have replaced air in the system. Keep an eye on it. It should fill as the engine warms and the coolant expands or pressurises depending on what coolant you use, and then returns back into the system as the engine cools after flight.

    I always check my coolant expansion bottle before and after every flight so I know the system is working and I use Evans coolant.

    I would suggest you don't remove the radiator cap as you can introduce air into the system.

    Mark

  • Re: Low Coolant Level

    by » 12 years ago


    Hi Joseph,

    Has the cooling system been worked on lately or have you done a coolant change?

    Filling the coolant on the 912 isn't like oil that needs to be forced into the system. It should gravity flow and fill most all the areas and the air will usually rise to the top. Depending on your installation and the radiator location air could be trapped, but should work it's way out after running a little while. If you haven't changed the coolant and just re-filled the system and you dropped 300ml then you may have a leak. Some of these can be hard to find because the high flow air around the engine blows it off. Check under the engine on the water pump housing weep holes for leaks. After you land remove the cowl(the system will be pressured up). Look around where the 90 degree elbows are on top of the engine for any tiny seepage.

    http://www.rotax-owner.com/information-reg/elearning-videos-reg/384-elbow


    Squeeze each coolant hose and especially on the hose before each clamp to see if you can milk and coolant from under the hose end where it slips over the metal fitting. It can seep here in flight and be hard to find because it can be blown off. Check for tightness on any worm drive clamps. Pulling the tank cap and checking the level won't induce air and is one of the checks for the annual and or 100 hr. A normal 912 coolant system usually takes 2/3 to 1 gal. of coolant depending on how the radiator is set up and if a thermostat is used.

    I see some coolant systems exchange coolant in the over flow bottle and some don't. Each plane is a little different and depends on its cooling ability. Some stay a little cooler and some hotter.

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


  • Re: Low Coolant Level

    by » 12 years ago


    Hi Joseph,

    I had a similar problem last year although I didn't lose coolant at quite the rate that you have. It turned out to be a tiny hole in the coolant radiator matrix. It only manifested itself when the engine was hot and the radiator had to be pressurised by a radiator repairer to find the hole. After welding, it has been fine.

    My coolant left a small red stain below the hole, this is how I located it.

    The coolant header tank cap has a clever valve arrangement that allows coolant out if necessary due to excessive expansion but it can draw coolant back in as it cools, clever!

    Kevin

  • Re: Low Coolant Level

    by » 11 years ago


    If your expansion bottle does not fill with some coolant when you reach operating temperature, then you have got air in the system and it needs topping up. Pour coolant into the expansion bottle when the engine is at normal operating temp and allow the engine to cool and suck the coolant into the system.

    Warm engine up and repeat if necessary until the expansion bottle fills as temp increases. This may take a few cycles to remove any air from the system.

    If possible, try and keep an eye on what is happening before and after you fly. If possible don't remove the radiator cap as you can introduce air into the system, although this should get replaced with coolant after the next cycle.

    Ideally you should have a small amount of coolant in the expansion bottle when cold.

    Mark

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