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I have been having problems with the coolant blowing out the vent in the recovery tank vent when climbing, at cruise it's not an issue the CHT all stay at 100deg C, on climb they go up to around 125 in around 2 min level out and they drop back to 100. i have changed to coolant using 50/50% this droped the temps by 10deg however the venting also happened at a lower temp. when it vents out the recovery bottle, the level in the bottle remains the same? I live in the tropics high hum, temps between 20-33 deg C. could this be air locks in the system blowing bubles back to the tank?
Aircraft is Skyfox same as kitfox however the radiator is in behind the engine under the top cowl, all the Kitfox that i have seen have it under the bottom cowl.
If i keep the CHT below 125 its not an issue but you can't maintane climb. Climb is normaly 500FPM at 5000rpm.

any ideas?
  • Re: Coolant comming out of header tank vent

    by » 12 years ago


    Hi LLoyd,

    The 125C (257F) coolant temp is a little too high and you may just be over heating and then as you say eventually venting out the top of the reservoir. 120C (248F) is the max for the 50/50 coolant. A couple of other items. Make sure you have the 1.2 bar pressure cap on the expansion tank. It is possible if the engine has been around a while you may need a new cap.
    I do think your just over heating, but the last two items need to be ruled out. You may be able to bring down temps by unloading the engine work load. If your prop isn't setup to get at least 5500-5600 WOT flat and level and it gets lower rpm at WOT that could be part of the problem or all of the problem. Something else you may need to do is get more air to the engine and or the radiators through the cowl. (I don't know how your system is set up)

    Try to get those temps down and I think the venting coolant will go away, so long as it isn't the cap.

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


  • Re: Coolant comming out of header tank vent

    by » 12 years ago


    thanks for the reply Roger i have just fitted a new 1.2 bar cap and it did improve the problem my ops manual states most favourable oil temp between 90 _ 110 deg c and max CHT of 150 deg C. i thought about fitting cowl flaps to try to get more air through the radiator. i never get any were neer 5800 rpm the prop i am using is 68D X 48P wooden do you think this is too corse?

    You can see in the photo that all the air has to come accross the hot engine before it gets to the radiator this dosn't help then it has to get out at the bottom of fire wall thats why i thought about the cowl flaps.
    Thanks

    Please note the engine is not that dirty now that is before i brought it all nice and clean now.
    kitfoxBernie003.jpg (You do not have access to download this file.)

  • Re: Coolant comming out of header tank vent

    by » 12 years ago


    Hi LLoyd,

    The prop numbers you gave me don't mean a whole lot as all props are a little different in design. What is important is that your engine rpm can get at least 5500 WOT. You don't have to get 5700-5800 WOT flat and level. What is the WOT rpm flat and level? You just don't want to be too low in rpm as that creates engines stress and heat.
    If the radiator is in the back is it possible to relocate the radiator or channel more air to it? Maybe just open a cowl opening a tad more for better cooling air flow may work?

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


  • Re: Coolant comming out of header tank vent

    by » 12 years ago


    Thanks Roger for the info, I set up some baffels to duct the air into the radiator ans stop it from bypassing, this worked a treat problem solved. thanks again for the help.

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