Whats normal top off/refill of hydraulic fluid (337B)?

[Jhogan0101]

yes. i did experience this when the nut on the elbow going into the rear hydro pump was loose and the threads wore out. it created a venturi situation and hydro fluid foamed out of the vent. took a while to find/understand what was happening.

anyway, this is different.

i have flown a couple times and it seems top off is minimal now. signs pointing to missing hydro fill screw causing the issue.

[wslade2]

Looks like the fill tube goes to the bottom of the reservoir. If so, missing that nut leaves tube open to a high pressure area from ram air. Can pressurize reservoir and possibly even bubbles the fluid introducing air or even foaming.

See attached link
Tube #68