Automatic Lubrication Systems FAQ
August 20, 2026
Cold weather thickens hydraulic oil, stiffens seals, and pulls moisture into reservoirs, and each problem shows up first at startup. Regular hydraulic service and repair before winter keeps equipment in unheated plants and yards from failing on the first cold morning.
Our West Michigan fluid power specialists see these cold-start problems every winter, and most of them can be prevented.
Here's what you need to know about running hydraulics in cold weather.
Why Hydraulic Oil Thickens in the Cold
Viscosity rises sharply as oil cools. An ISO VG 220 oil can climb to at 32°F, far above its normal operating range.
Pump makers set cold-start limits for this reason. One Bosch Rexroth piston pump, for example, allows a .
Cavitation and Pump Starvation
When thick oil cannot reach the pump inlet fast enough, the pump starves and cavitation can follow. The damage from a restricted pump inlet can be catastrophic.
Filters suffer too, since cold oil raises the pressure drop and can open the bypass valve or even rupture the element. Good lubrication practices follow the same rule: the right viscosity at the right temperature.
Seals Harden and Start to Leak
Cold starts and cold operating temperatures can make seals brittle. A hardened seal that leaks oil can also let water and dirt into the system.
Seal makers offer compounds for equipment that works outside all winter.
Condensation Puts Water in the Oil
As equipment cools during shutdown, moisture in the reservoir air can condense into free water. Water in oil leads to corrosion, thinner lubricating films, and even .
Our guide to hydraulic fluid cleanliness explains how water also oxidizes oil and raises its acid number. Desiccant breathers help keep moist air out of the tank in the first place.
Warm the System Up Before Full Load
Let the oil warm up before running at full pressure, starting with low-speed, low-pressure cycles of each function. Always follow the equipment manufacturer's warm-up recommendations.
For equipment in unheated buildings, a properly sized tank heater can bring oil up to temperature before a shift starts. MFP can build a custom hydraulic power unit that meets the specifications your system requires.
Choose the Right Fluid for Winter
Fluids with a higher viscosity index change less as temperatures swing, which makes them a better fit for cold starts. Match the grade to both the pump maker's viscosity limits and the coldest temperature your equipment will see.
Filtration analysis from MFP can show whether your fluid and filters are ready for winter. Our hydraulic components inventory covers pumps, valves, filters, and coolers.
Frequently Asked Questions
What temperature is too cold to run a hydraulic system?
There is no single cutoff temperature. The real limit is the point where your oil passes the pump maker's maximum cold-start viscosity, which depends on the fluid's grade and viscosity index.
For example, a premium ISO VG 22 oil with a viscosity index of 100 might have a pour point around -17°F. Thicker grades reach their limits at much warmer temperatures.
Can you mix hydraulic fluids for winter?
Mixing oils with different additive packages is not recommended, because the additives can work against each other and lead to corrosion or wear. If a mix happens with matching viscosities, it may get by for a short time.
In that case, watch for sludge and foaming, test the oil more often, and flush and change it as soon as you can.
How can you tell if hydraulic fluid has water in it?
Cloudy oil is the clearest sign, because it means water has passed the saturation point of roughly 200 to 300 ppm in mineral oil. A hot-plate crackle test gives a rough check, while lab testing gives precise numbers.
MFP's filtration analysis service checks particle counts and recommends maintenance for your pumps, filters, and fluids.
What should you look for in a hydraulic tank heater?
Choose a heater with a low watt density, no more than about 4.5 watts per square inch, so it warms the oil without burning it. Heaters built for water run far hotter and can carbonize hydraulic oil.
Size the heater for your tank volume and the temperature rise you need, and allow at least an hour of heating before startup.
Can MFP train our maintenance team on hydraulics?
Yes, MFP offers Basic Hydraulics and Advanced Hydraulics training classes at our Hudsonville facility. The courses cover everything from basic hydraulic repair and systems maintenance to advanced fluid power technologies.
Classes are held in the evening and have typically run twice a year, in the spring and fall. Contact our team for the current schedule.
Keep Your Hydraulics Running This Winter
Cold weather does not have to mean cold-start failures. The right fluid, a steady warm-up routine, and clean, dry oil go a long way.
MFP is a West Michigan industrial automation supplier with 24-hour hydraulic service. Call MFP Automation Engineering today at (616) 538-5700 or request a quote online.