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912ULS Overheating

in 912 / 914 Technical Questions 12 years ago
After running cooler than factory normal for 450 hrs . my engine is suddenly overheating and very quickly. It's fine at idle and when I run it up for ignition check but on takeoff at 5400rpm the water temp is approaching 280F by the time I'm at 800AGL. CHT is pushing 300F at this point. If I back it downtown 4000rpm the temp will slowly fall. OAT this afternoon was 55F. Coolant level is normal (Evans). This engine has routinely flown in 90F weather with no problems. As it happened suddenly and all else appears normal I suspect the water pump or expansion chamber. Are there some tests I can try to pinpoint the problem?
Thanks - Mike

  • Re: 912ULS Overheating

    by » 12 years ago

    Hi Mike

    The first place I would check is the water pump. Remove the two screws that hold the inlet hose on to the water pump housing and check all the vanes on the impeller are present and correct and that the impeller turns with the engine.
    This is sealed with an O-ring and should be ok to remove without replacing the o-ring.

    Don't forget to drain your coolant into a clean bucket first and then filter it before pouring it back in.

    Before you do this though, check that the radiator is clear and not blocked with debris, and there are no damaged or restricted radiator hoses.

    Mark
    Thank you said by: Michael Nault
      
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  • Re: 912ULS Overheating

    by » 12 years ago

    Thanks Mark. In order to remove the inlet fitting I'm going to have to move or maybe remove my muffler which is immediately behind the fitting. Right now I can't get a wrench on the bolts because it's so close. I'm OK with doing this but only after I've eliminated other possibilities. How often do these impellers fail?
    Is it possible that the pressure cap on the expansion tank could be the problem? I blew out the tubing to the overflow tank and it's clear.

    Should everything continue to point to the pump and I decide to remove it the Rotax tool to remove the impeller is $200. Is this absolutely the only tool that will work and if so, do you know of anyone that might rent me one?
    thanks
    Mike
      
    Report

  • Re: 912ULS Overheating

    by » 12 years ago

    Have you checked the rad ? Is it allowing coolant to flow thru it freely ?

    Do you have a thermostat in your coolant setup? Bad thermostat possibly?

    Any work recently done before the problem occurred?
      
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  • Re: 912ULS Overheating

    by » 12 years ago

    Hi Micheal

    As you say the water temp has suddenly started over heating after running cool for 450 hrs I wouldn't expect the rad to be blocked.It would be easy to check but I would imagine it would become blocked over a period of time and you would notice that it would start to run hotter over time and not over night.

    I am taking it for granted that you have a standard set up and no thermostat is fitted, although this would be the first place to look if you have.

    I am also presuming that you haven't had any maintenance done recently as this would be an obvious place to start looking.

    The way you describe it, it sounds like it has happened "out of the blue" and so I would expect something has failed, and as the coolant circuit is very simple, it points to the pump.

    I have seen an impeller that was stripped of the vanes after someone dropped a 10mm socket into the radiator and left it there. If the vanes are damaged, a $200 tool will not be of any use, and if the vanes are ok and the impeller turns with the engine, the problem lies somewhere else.

    I suggested that you check it this way as you only have to unscrew two cap head screws, but I didn't realise it was in an awkward position.

    The rad cap won't have anything to do with this, even more so the fact that you are using Evans which doesn't require a pressurised system.

    Good luck and keep us updated.

    Mark
    Thank you said by: Michael Nault
      
    Report

  • Re: 912ULS Overheating

    by » 12 years ago

    Radiator is clear
    No thermostat
    No maintenance on engine
    When I flushed the system I replaced the Evans with 50/50 conventional.
    I'll remove the muffler and check the impeller vanes and go from there.
    thanks much Mark!

    Mike
      
    Report
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