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Hi - 30hr engine - my water temp seems to be very consistent around 80-85 degC, I've never seen them higher than this. This seems to me to be running cold? Also there has been a drop in the coolant and a couple of small puddles under the machine a few hours back but nor recently.

I'm very wary because I had a 912 previously that ran similarly cold until eventually the rad cap finally failed and it dumped all it's coolant in flight. I'm wondering if this is a sign of a suspect pressure cap or if it's just normal behaviour. Air temps (in flight) have been around 10degC. Oil temps usually sat at around 90degC (consistently 5 to 10 deg hotter than water).

I've been told that the slight need to top up (once from min to max) and the small puddles of overflow can be caused by air in a newly filled system bleeding out - this would be consistent with the the loss of coolant having essentially stopped recently.

Any thoughts? Is this normal or indicative of an issue? Should I shell out £80 on a new pressure cap just in case?
  • Re: Water Temps - Issue or not?

    by » 11 months ago


    Here's what it looked like at preflight today - it's not losing a lot of water but down again to about midway between max and min. Are there any other likely explanations? How likely are Rotax to accept that's this is a warranty issue?
    RotaxHeader.jpg (You do not have access to download this file.)

  • Re: Water Temps - Issue or not?

    by » 11 months ago


    Well, it appears that the cap is leaking.
    The leak will be at the outer seal which never has any pressure behind it.
    Look closely to make sure the gasket and seat are clean.

    The cap is nothing special. it is repurposed from the automotive world.
    If you do not want to spend big bucks on the Official Rotax cap;
    A BMW 17112345074 Cap appears to be identical.
    The Triumph T2108005 is also reported to fit.

    I just tried to swap my Rotax cap into a Subaru Forester in the driveway.
    The Rotax cap Fits in the Subaru but the internal seal of Subaru's cap is too large to fit on the Rotax tank.
    The two caps have different pressure ratings so this is not a surprise,
    I am sure there are many caps available from your local Auto Parts Store that would also fit.
    Be sure the pressure rating is correct. 1.2bar = 18psi = 120kpa

    I expect to get flamed for this heresy! :evil:

    Bill Hertzel
    Rotax 912is
    North Ridgeville, OH, USA
    whertzel1@yahoo.com
    Clicking the "Thank You" is appreciated by all.

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