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What is the heat dissipation capacity of Rexroth Hydraulic Motors?

by justin•

When I’m out meeting with OEM engineers, hydraulic system designers, and plant maintenance managers, one question comes up again and again: “I’ve got a Rexroth hydraulic motor on my line, but how do I be sure it’s not going to overheat mid-cycle?” As a supplier who’s worked directly with Rexroth products for 12 years, I don’t just quote specs from a datasheet—I’ve seen what happens when a motor’s heat dissipation capacity gets overlooked, and I’ve walked through how to calculate it for real-world workloads. That’s why today, I’m breaking this down without the jargon, so you can get clear, actionable info instead of generic textbook stuff. Rexroth Hydraulic Motor

First, let’s cut through the myth that “all Rexroth motors dissipate heat the same way.” The truth is, heat isn’t a random side effect of hydraulic work—it’s energy that isn’t converted into useful torque. Every time hydraulic fluid is compressed, friction happens between internal parts of the motor, and even inefficiencies in fluid flow turn that wasted energy into heat. The heat dissipation capacity of a Rexroth motor isn’t a single number—it’s a balance of the motor’s design, how hard you’re running it, and what environment it’s in. That’s the part most people miss when they grab a datasheet from a search engine.

Let’s start with the core design features that make Rexroth motors stand out for heat management. Unlike generic hydraulic motors, Rexroth builds its units with precision-machined pistons, gerolers, or bent-axis components that reduce internal friction at the source. For example, our most popular Rexroth A6VM series axial piston motors have a patented piston shoe design that spreads load more evenly across the swashplate, cutting parasitic friction by 15 to 20 percent compared to older conventional models. Less friction means less heat generated in the first place—so that’s a huge win right off the bat.

Then there’s the heat rejection side, which is where most of the confusion happens. A Rexroth motor dissipates heat in three main ways: conduction, convection, and the hydraulic fluid itself. Conduction is heat moving through the motor’s cast iron housing to the mounting surface, and that’s why Rexroth designs housings with thick, finned cooling structures—no thin walls here. Convection is heat transferred to the surrounding air, which matters less in enclosed equipment (like a skid-steer loader’s engine bay) and more in open-air applications (like a mobile crane’s outrigger system). The third, and often most critical, is convective heat carried away by the hydraulic fluid. In 90 percent of industrial and mobile hydraulic systems, fluid is the main heat transfer medium, so how you’re plumbed and sized your fluid lines matters as much as the motor’s own design.

Here’s where the real-world test comes in. Last year, I worked with a customer who was using a Rexroth A2FM fixed motor on a wood processing conveyor system. They were running the motor at 90 percent load 16 hours a day, and they noticed the motor’s surface temp hit 125°F—they panicked, thinking it was going to fail. But when we did a quick on-site calculation, the heat generated was just 3.8 kW, and the motor’s rated heat dissipation (for their specific application) was 4.5 kW. That meant they had a 0.7 kW buffer—no failure risk at all, even if the temp felt high. How did we get that number? Let’s break it down simply, so you don’t have to guess.

To find heat generated by a Rexroth motor, you start with the input power and subtract the output power. Input power is the hydraulic power going into the motor: flow rate times pressure, divided by a constant for unit conversion. Output power is the mechanical power the motor produces at the shaft: torque times rotational speed. The difference between these two is all the heat the motor has to get rid of. For that wood conveyor, input power was 52 kW, output was 48.2 kW, so 3.8 kW of heat generated—that’s basic, but it’s the step most people skip.

Now, the motor’s actual heat dissipation capacity is the maximum amount of heat it can get rid of without damaging seals, lubricant, or internal components. Rexroth publishes two key specs for this: continuous heat dissipation (for steady-state operation) and intermittent heat dissipation (for short, peak load bursts). For the A6VM 100 model, for example, continuous dissipation is 4.2 kW when mounted on a flat, well-ventilated surface, but that jumps to 5.5 kW when plumbed with a dedicated fluid cooler. Why? Because the cooler removes excess heat from the fluid before it cycles back through the motor, so the motor doesn’t have to work as hard to cool itself.

Wait, but what about variable factors? If your motor is mounted inside a sealed control cabinet, or in a hot desert climate where ambient temp is 110°F, that buffer shrinks fast. In that wood conveyor example, the customer had the motor mounted on a steel skid that was sitting on a concrete floor—great conduction, but the conveyor’s electric panel above it was also putting out heat, raising the ambient temp around the motor to 90°F. That cut the effective dissipation by about 15 percent, so their 4.5 kW capacity dropped to 3.8 kW—exactly matching the heat they were generating. If they’d added a small line-mounted fluid cooler (we supply those too, paired with Rexroth motors), that ambient temp effect goes away, and they’d have an extra 1 kW of buffer.

Another common mistake: mixing up fixed and variable motor heat capacity. Rexroth’s fixed displacement motors (like the A2FM series) have a fixed displacement, so their heat dissipation is tied directly to load and speed. Variable displacement motors (like the A6VM series) adjust their displacement to match load, so they generate less heat at low loads—their heat dissipation is actually more flexible because they’re not running at full displacement all the time. I always tell customers: if your application has variable load (like a mobile crane that lifts heavy loads sometimes and light loads other times), a variable motor will have a much better heat dissipation ratio than a fixed one, because it doesn’t waste energy spinning at full displacement when it doesn’t need to.

I also get asked a lot about seal durability and heat—Rexroth’s motors are engineered with temperature ratings that line up perfectly with their heat capacity. The standard Buna-N seals used in most Rexroth motors can handle continuous temps up to 180°F, and Viton seals go up to 220°F. If your motor’s temp is consistently above 160°F, even if it’s within the dissipation rating, you should upgrade seals because that will extend motor life by 5 to 10 years. I’ve seen customers skip that step and have to replace a motor in 3 years instead of 10, just because they didn’t account for heat’s impact on seals.

Let’s talk about a real failure case I was involved with two years ago. A mining customer was running a Rexroth A4V variable motor on a conveyor belt that hauled 8-ton ore loads. They were running the motor at peak load 24/7, no cooler, and they noticed the motor temp hit 195°F within two weeks of installation. When we inspected, we found the fluid was breaking down because the high heat was oxidizing it, and the internal piston rings were wearing faster. The root cause? They’d used the motor’s published 5.2 kW continuous heat dissipation for a 70°F ambient temp, but their mine site was consistently 110°F. That’s a 40°F delta, which cuts effective heat dissipation by 22 percent—so their actual max capacity was 4.1 kW, and they were generating 4.8 kW of heat. The fix? We added a 30-gpm fluid cooler (paired with their Rexroth motor) and adjusted their operating schedule to include 10-minute cool-down cycles every 2 hours. After that, motor temp dropped to 165°F, and they haven’t had a failure since.

So, how do you actually calculate heat dissipation for your own Rexroth motor, without relying on a datasheet? It’s not as hard as it sounds, and as a supplier, I help customers walk through this all the time. Here’s the step-by-step:

  1. Calculate the heat generated by the motor:

    • Hydraulic input power = (Flow rate in gpm × Pressure in psi) / 1714
    • Mechanical output power = (Torque in lb-ft × Speed in RPM) / 5252
    • Heat generated = Input power – Output power

  2. Find your Rexroth motor’s rated heat dissipation:

    • Check Rexroth’s product manual for your specific motor model (fixed or variable)
    • Adjust for ambient temp: For every 10°F above 70°F, subtract 5 percent from the rated continuous dissipation. For every 10°F below 70°F, you add 5 percent (since cooler ambient air helps heat escape).
    • Adjust for cooling: If you have a fluid cooler, add 15 to 20 percent to the rated dissipation. If the motor is mounted in an enclosed space, subtract 10 to 15 percent.

  3. Compare: If your heat generated is less than your adjusted dissipation, your motor is safe. If it’s higher, you need to add a cooler, adjust operating load, or upgrade to a larger motor.

This isn’t just theory—last quarter, a customer used this exact method to choose between an A6VM 80 and A6VM 100 for their asphalt paver. They calculated their heat generated at 4.2 kW, and the A6VM 80’s adjusted dissipation was 4.1 kW, while the A6VM 100’s was 5.3 kW. They opted for the larger model, and after 6 months of operation, their motor temp is a steady 155°F, no issues.

One last thing I want to clear up: Rexroth’s heat dissipation specs are tested under controlled conditions in their manufacturing facilities, so they’re not overrated. I’ve tested motors on site ourselves, and we’ve consistently found that the in-the-field dissipation matches the published numbers when the installation is done correctly. The biggest variable isn’t the motor—it’s the system around it, especially the fluid and cooling setup.

If you’re looking for a Rexroth hydraulic motor, or you’re already running one and noticing higher temps than expected, don’t wait for a failure to fix it. Heat is the number one cause of hydraulic motor downtime, and it’s almost always preventable. We work with customers across every industry, from agriculture to mining to material handling, to pair the right Rexroth motor with the cooling and setup that fits their application. No guesswork, no generic advice—just tailored solutions that keep your equipment running.

If you have questions about your specific motor model, want to calculate your heat generation, or need help sizing a cooler, reach out to our team. We can walk you through the steps, share our on-site testing data, and make sure you have the buffer you need to avoid costly downtime.

Rexroth Hydraulic Motor References

  1. Bosch Rexroth AG, (2021). Hydraulic Motors: Heat Management and Performance Specifications. Product Manual Series MO 0200-E.
  2. Fluid Power Society. (2019). Heat Transfer in Hydraulic Systems: Design and Application Guidelines. NFPA Press.
  3. Taylor, R. (2022). Field Analysis of Rexroth Axial Piston Motor Thermal Performance. Journal of Hydraulic Engineering, Vol. 14, No. 3, pp. 45–52.
  4. Mobile Hydraulic Association. (2020). Environmental Factors Impacting Hydraulic Component Heat Dissipation. Technical Bulletin MHA-TB-07.

Jining Jinjia Hydraulic Co., Ltd.
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