Liquid Fill

What liquid fills automatic window openers in greenhouses? Mine fell apart the other day when fixing a pane?
I have tried 3-in-1 oil and it does open a little, does hydraulic oil expand better under heat? The heat inside the greenhouse controls the automatic opener not by electricity or by any other means. I even tried water hoping that as the greenhouse warmed up it would make the water expand thus opening it, that failed completely though and I shall give hydraulic oil a try and see how it goes for now and thanks. I will give full marks to the answer that gets the thing working again.
Hydrolic oil
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