I have my diesel transfer pump I use for pumping out of my slip tank into the equipment I believe it is fill right. Push the little sliver button switch and it runs till you shut it off type. Think it will work to pump a 46 weight hydraulic oil out of the 55 gallon drum ?
I've done it with a 110volt one, but never a 12volt one. Might check that the pump motor isn't getting too warm as your running. Stop halfway and let it cool down.
Maybe if its pretty warm. I tried 10wt hyd oil when it was around 50F, pulled motor down and got really hot fast.
Copy will put the mr heater on the barrel. And give it a shot I’m open to taking breaks to to let the motor cool down.
I use a hand crank barrel pump all the time. It was meant for gasoline but handles hydraulic oil and diesel all the time.