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The Bobcat E85 and Its Role in Mid-Size Excavation
The Bobcat E85 is a compact excavator designed for high-performance trenching, grading, and utility work in confined spaces. With an operating weight of approximately 18,000 pounds and a 65-horsepower turbocharged diesel engine, the E85 sits at the top of Bobcat’s compact excavator lineup. It features load-sensing hydraulics, selectable work modes, and auxiliary hydraulic circuits for attachments like thumbs, hammers, and tilt buckets.
Bobcat, founded in North Dakota in 1947, has become a global leader in compact equipment. The E85 reflects the company’s push toward Tier 4 compliance, operator comfort, and hydraulic precision. However, like many machines with high-pressure hydraulic systems, the E85 can exhibit audible pump noise during cold starts—especially in temperatures below freezing.
Cold Weather Effects on Hydraulic Systems
Hydraulic fluid viscosity increases significantly in low temperatures. This thickened fluid resists flow, causing the pump to work harder and potentially cavitate. Cavitation occurs when vapor bubbles form in the fluid due to low pressure at the pump inlet, then collapse violently—producing noise and wear.
Symptoms of cold-induced hydraulic noise include:
In 2023, a contractor in Minnesota reported that his E85 emitted a high-pitched whine for the first 15 minutes of operation during sub-zero mornings. After switching to a lower-viscosity hydraulic fluid and installing a reservoir heater, the noise was reduced and warm-up time shortened.
Diagnosing Hydraulic Pump Noise
To determine whether the noise is normal or indicative of a problem:
Preventive Measures and Fluid Management
To minimize cold-weather hydraulic issues:
Conclusion
Hydraulic pump noise in cold weather is a common issue on the Bobcat E85 and similar excavators. While some noise during warm-up is normal, persistent or excessive sound may indicate cavitation, fluid restriction, or suction line failure. With proper fluid selection, warm-up procedures, and preventive upgrades, operators can reduce noise, protect components, and maintain reliable performance in winter conditions. In hydraulic systems, silence is golden—and warmth is the key to achieving it.
The Bobcat E85 is a compact excavator designed for high-performance trenching, grading, and utility work in confined spaces. With an operating weight of approximately 18,000 pounds and a 65-horsepower turbocharged diesel engine, the E85 sits at the top of Bobcat’s compact excavator lineup. It features load-sensing hydraulics, selectable work modes, and auxiliary hydraulic circuits for attachments like thumbs, hammers, and tilt buckets.
Bobcat, founded in North Dakota in 1947, has become a global leader in compact equipment. The E85 reflects the company’s push toward Tier 4 compliance, operator comfort, and hydraulic precision. However, like many machines with high-pressure hydraulic systems, the E85 can exhibit audible pump noise during cold starts—especially in temperatures below freezing.
Cold Weather Effects on Hydraulic Systems
Hydraulic fluid viscosity increases significantly in low temperatures. This thickened fluid resists flow, causing the pump to work harder and potentially cavitate. Cavitation occurs when vapor bubbles form in the fluid due to low pressure at the pump inlet, then collapse violently—producing noise and wear.
Symptoms of cold-induced hydraulic noise include:
- Loud whining or groaning from the pump area
- Delayed response from boom or arm functions
- Increased vibration through the control levers
- Audible pitch change as fluid warms and thins
- Temporary loss of auxiliary hydraulic power
In 2023, a contractor in Minnesota reported that his E85 emitted a high-pitched whine for the first 15 minutes of operation during sub-zero mornings. After switching to a lower-viscosity hydraulic fluid and installing a reservoir heater, the noise was reduced and warm-up time shortened.
Diagnosing Hydraulic Pump Noise
To determine whether the noise is normal or indicative of a problem:
- Check fluid type and viscosity rating. Bobcat recommends ISO 46 hydraulic oil for moderate climates, but ISO 32 may be better for cold regions.
- Inspect suction lines for cracks, kinks, or loose clamps. Air ingress can cause cavitation and erratic pump behavior.
- Examine filters and screens for blockage. Cold fluid may restrict flow through clogged elements.
- Monitor pump temperature and noise duration. If noise persists beyond warm-up, internal wear may be present.
- Use a stethoscope or sound probe to isolate the noise source—pump, relief valve, or motor.
- Replace suction hose if it shows signs of internal collapse
- Use two clamps per hose end, spaced 180 degrees apart
- Install a fluid heater or keep machine in a heated enclosure
- Let engine idle for 10–15 minutes before engaging hydraulics
- Avoid full throttle operation until fluid reaches operating temperature
Preventive Measures and Fluid Management
To minimize cold-weather hydraulic issues:
- Use multi-grade hydraulic fluid rated for low-temperature operation
- Store machines indoors or use thermal blankets on reservoirs
- Install inline heaters or block heaters to pre-warm fluid
- Avoid sudden joystick movements during cold starts
- Schedule fluid analysis annually to monitor contamination and viscosity
- Retrofit reservoir heater with thermostat control
- Add hydraulic fluid temperature sensor with cab display
- Use synthetic hydraulic oil with stable viscosity across temperature ranges
- Install quick-drain valve for easier fluid changes
Conclusion
Hydraulic pump noise in cold weather is a common issue on the Bobcat E85 and similar excavators. While some noise during warm-up is normal, persistent or excessive sound may indicate cavitation, fluid restriction, or suction line failure. With proper fluid selection, warm-up procedures, and preventive upgrades, operators can reduce noise, protect components, and maintain reliable performance in winter conditions. In hydraulic systems, silence is golden—and warmth is the key to achieving it.
