During the New Mexico winters, temperatures can get very low. On those very cold nights, after I draw water for the sheep, I just know that the residual moisture in the frost-free hydrant will freeze before it dissipates from the inside. The next morning, the hydrant is indeed frozen. The handles of most hydrants are painted, so if the sun shines, the hydrant will thaw and function again by the end of the day. However, if I cannot wait for the sunshine, I have to thaw the hydrant some other way. A small bucket of hot water over the hydrant usually will solve the freeze. I complained about my frozen hydrants once to my father-in-law who had a lifetime of experience farming in bitter cold weather. He told me, in his understated way, “I put a little oil on the plunger once-in-a-while. That seems to help.” I took his advice, and indeed, I have eliminated frozen hydrants on cold mornings.
All hydrants have a rod that moves up and down inside the hydrant pipe. When the handle is lifted, you will see this rod move upward through its attachment to the lift handle. When you close the hydrant, the rod moves back downward. By adding enough oil to coat the exposed rod and a few drops more to penetrate downward, the inside of the hydrant gets a thin coating of oil. The oil adheres to the metal and repels water. In the cold, the oil repels water, and any residual moisture cannot adhere to the metal parts and freeze the mechanism. Furthermore, the hydrant handle and mechanism will function more smoothly all the time. The oil needs to be a lightweight oil. I prefer automatic transmission fluid (ATF) because it is lightweight and ATF is an excellent penetrating oil. After applying some drops of oil to the mechanism, you might see a little oil film on the top of the first bucket of water you draw. I discard that first gallon, and I don’t see any more oil in the water after that.