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Rough running, 3500 - 4500rpm, Rotax 912

in 912 / 914 Technical Questions 13 years ago

  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 13 years ago

    Ahh Haa, the old disappearing coolant. Been there a time or two.
    Here is what I have usually found. Unless you have puddles of coolant on the floor at the back of the cowl from a water pump seal leak then here is the usual culprit.
    The first time this happened to me it took for ever to figure it out. The hose clamps that may be of the screw type will loosen over time due to heating and cooling (expansion and contraction)of the hose and crushing of the hose under the clamp. The fluid doesn't seem to leak just sitting there, but when you fly and the heat and pressure build the coolant seeps under the clamps and the high pressure air flow around the engine just blows it off. So when you land and look at the system after a few flights you can't figure where the coolant went. There are no tattle tale signs. I happened to find it on cylinder #2 one day when I was squeezing the hose I saw a drop of coolant come out. The heat off the engine also keeps you from finding this after a flight because it evaporates fairly quickly.
    Tighten all screw type hose clamps on your coolant system. I would bet this will take care of your disappearing coolant. Every inspection that is the one thing I always do on everyone's plane. I put a screwdriver or socket on every clamp and check them.

    They may be finger tight, but wrench loose.

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

      
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  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 13 years ago

    Coolant comsumption measured at 80l/hr. This means the engine will have a dry header tank before it runs out of fuel!
    No external loss of coolant - the engine is in s trike with low speed swirling airflow - and from experience any external coolant leak is quite easy to spot (and believe me, I have been looking!).

    So - I am awaiting a response from the Rotax importer about what happens now.

    Andy Buchan
      
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  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 13 years ago

    Hi Andy,

    You may not ever see any coolant if it leaks from a hose or fitting. The air flow will blow it off. I have done this long enough to see this many times and you can chase your tail forever. Every singe hose end and clamp needs to be checked. All screw type hose clamps need to be checked. After you land and there is still pressure in the system squeeze each hose fairly hard and you may find a leak. Your low air flow is more than you think. All it takes is a slight blow from your mouth and you can blow coolant off and if it doesn't leak to where it can puddle then it's a going to be gone no matter how slow the air flow. My money is still a leak around an hose end and especially on one that is a screw clamp and not a constant compression clamp. Those can leak too if not applied correctly.

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

      
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  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 13 years ago

    Andy, check your cap and see if it's a .9 (13#), Rotax is now recommending a 1.2 (17#)also a coolant recovery bottle if you don't have one already.
      
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  • Re: Rough running, 3500 - 4500rpm, Rotax 912

    by » 13 years ago

    Roger,
    Hi - thanks for your comments but believe me, there is no external loss of coolant. Hose clips were checked early on as you suggest, but I have checked again. Absolutely no sign of coolant being lost externaly.

    Ted.
    Thanks for your comments - The engine is less than a year old so has the current spec of coolant cap which I am pretty sure is 1.2 bar, and it has an expansion tank fitted.

    Other similar engine / aircraft have the expansion tank fill as the coolant heats up: this engine does not do this. Instead, any coolant in the expansion tank gets sucked back into the header tank when the engine cools and the coolant level in the header tank then continues to drop with further useage.

    The current situation is that the engine has been returned to the aircraft manufacturer who in turn are involving the Rotax importers. Drinking coolant is more easy to quantify than rough running - but presumeably the two problems are connected?

    I will post again when a final solution has been found, but the problem may well be a one-off of a porous casting?

    AndyB
      
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