How Convenient: 3 ton floor jack?

Floor jacks can be a PITA. Other than actual hardware problems, the biggest issue is either low fluid, or the fluid level/ air "level." What happens is this:

Jacks are supposed to operate "unvented." what this means is, that as you pump it up, fluid is pumped from the reservoir which is sealed by the unvented filler cap, into the ram. So it starts a partial vacuum in the reservoir. If fluid is low, it will run out of fluid and pump air. If there is too much fluid it will cause too much vacuum, and the pump will not fill, and cease pumping.

Frankly on two of my cheap-*** Chineseoationized jacks, one of which is an old school HUGE heavy deal, "I just left the filler cap loose." and the thing worked that way for years.