Hi Guys, I have a Zenair with a 912 ULS in it, done 300hrs.

On shutting after my last flight, on a particularly warm day, I noticed a hissing noise from under the cowling. Unfortunately I was unable to get the cowling off before it stopped. The oil temp had reached 120C and the coolant 90C during the flight and there had been no other indications.

The next day I checked the levels and found that there was no loss of either coolant or oil.
My thoughts are that the engine was hot and that when the engine stopped heat was absorbed into the coolant and dispelled into the coolant bottle, displacing some of the air, which then escaped via the bottle air hole, making the hissing noise. But I'm not convinced - any ideas ?

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