If you get cold and stiffer in the winter, you shouldn’t be surprised if hydraulic fluid does the same. While it doesn’t change form the way liquid water does in the cold (think snow and ice), hydraulic fluid does change when the temperatures drop. This means that some special attention is required when using equipment that incorporates hydraulic components; while the information below relates specifically to chippers, many of the principles apply to all hydraulic equipment.

“Hydraulic fluid will get more viscous when cold,” explains Boyd Schwarting, fluid power/electrical systems department manager with Bandit Industries. This thicker “means that when the system starts up for the first time on a cold day, it may be sluggish in operation if work is done before the fluid warms up,” says Schwarting. He notes that typically there are bypass valves around critical components (filters, coolers) to allow oil to pass freely around them when cold. “Typically, OEM’s will recommend a warm up period after start-up on a cold day.”

It’s not just a matter of the hydraulics performing more sluggishly. Without proper warm up, operation can cause damage to the system. “The cold weather makes the oil a lot thicker, so if you do not run the unit to heat the oil prior to chipping you could cavitate the pump and accelerate the normal wear on the o-rings, seals, fittings and hoses,” explains Casey Gross, tree care products sales manager with Morbark. “If at all possible, it’s best to store the equipment inside to avoid the added time to warm all the components up prior to going to work. There are heating pads as options that can be added to the hydraulic tanks that will keep the oil warm as well.”

The M15R TorqMax Plus Photo: Morbark

“Lower temperatures can put additional stress on pumps that have to draw the fluid in when cold,” agrees Bandit’s Boyd Schwarting. “It is best to let the machine idle for a few minutes to warm the fluid up before putting the machine to work,” he emphasizes. Additionally, Schwarting cautions, “you should not start the machine if the temperature is below the fluid pour point.”

Fortunately, most hydraulic fluids have a “pour point” (the temperature below which the fluid will lose its flow characteristics) well below zero degrees. There are even some arctic hydraulic fluids specifically designed for use in extremely cold weather, but be sure they are compatible with the equipment you are using. Schwarting points out that, in most cases when the temperatures drop below the pour point of the hydraulic fluid, the engine in the equipment won’t start anyway. “We recommend engine and hydraulic tank heaters be used when the outside temperatures reach below freezing to help eliminate this worry,” he says.

Taking these precautions during cold winter months will ensure that hydraulic equipment performs better and lasts longer. And what about when the temperatures really plummet? Casey Gross with Morbark offers a good rule of thumb for winter operations: “If it’s too cold for the crew to be out working, it’s the same for the equipment.”

Tips From Bandit Industries For Operating Hydraulics in Cold Weather

  • Always let the machine warm up before putting to use.
  • Use engine and hydraulic tank heaters to keep the fluids warm.
  • Do not start a cold engine/system and immediately put it to work before it warms up a little.
  • Use the proper oil for your climate, the oil a machine uses in the south can be used year around. Normally in southern climates an ISO grade 68 fluid is recommended for summer months but this fluid performs very well in their winter months. In the north, you may want to run a more viscous fluid in the summer months (such as the ISO 68 grade) and a lighter fluid in the winter months (an ISO 32 or 46 grade) to help the system operate at its peak performance.