DO NOT use brake fluid. If you do you can kiss every moving
part of the log splitter, except the motor, goodby in a few months. You can safely use A.T.F. type A. It is a little thinner than type F if you want to split at 20 below. It is not a good idea mixing fluids but you can
completely drain and flush your system and reinstall
A.T.F.

Another fluid that you could use is a 'universal hydraulic fluid' available at Tractor Supply, Farm & Fleet, or other farm supply stores. UHF is typically used as an all-in-one gear lubricant and hydraulic fluid in newer farm tractors.

Actually the day after I posted I ran into somebody who gave me the straight scoop. Matter of fact he gave me a gallon of the same stuff you recommended formula 1, thanx. Hey kalining, what the heck are you doing here? You belong in the heat and A/C forum! TRAITOR! :-) Hey at my age the only splitting I'm gonna do at 20 below is splitting for Florida!

MR. HAVAC. I'd ask the same question :)
We are too cold for A.C. not hot enough for heat. I've got
too much time on my hands. thought i'd sniff around and
low and behold there you were. just had to step in. So
how are you ? I've actually got 7 cords to split so i guess
it will keep me off the beer for a few days. Take care all you wood splitting guys out there. Winter is coming. I've been burning since the last 2 weeks in august. Trying to get my garage finished before it snows, which in this place should be in about 2 hours. See you back at the A.C.
site.