Pump Overheating: Causes & Prevention

Why Pumps Overheat

A centrifugal pump converts electrical energy into hydraulic energy (flow and pressure). Not all the input energy becomes useful work — some becomes heat. Under normal operating conditions, the pumped liquid carries this heat away. But when the pump operates abnormally, heat accumulates faster than it's removed, and the pump overheats.

The maximum acceptable bearing housing temperature is typically 80°C, or 40°C above ambient. Above this, the lubricant breaks down, bearings fail, and seals are damaged.

Causes of Overheating

• Operating at very low flow (shutoff): The #1 cause. When the discharge valve is nearly closed, the pump is doing almost no useful work — nearly all the input energy becomes heat. With no flow to carry the heat away, the pump body and liquid heat up rapidly. Fix: never operate a pump below its minimum continuous flow rate (typically 30% of BEP).
• Cavitation: Cavitation generates localised heat at the impeller where bubbles collapse. Severe cavitation can raise the pump temperature significantly. Fix: address the NPSH issue causing cavitation.
• Bearing failure: Worn or contaminated bearings generate excess friction heat. A failing bearing can heat the bearing housing to 100°C+ within minutes. Fix: monitor bearing temperature and vibration; replace bearings at the first sign of trouble.
• Lubrication problems: Over-greasing traps heat inside the bearing housing. Under-greasing causes metal-to-metal contact. Wrong lubricant grade doesn't provide adequate film strength. Fix: follow the manufacturer's lubrication schedule and quantities.
• Misalignment: Shaft misalignment between pump and motor causes the coupling to flex with every revolution, generating heat. Fix: laser-align the coupling.
• High liquid temperature: If the pumped liquid is already hot (e.g., boiler feedwater at 90°C+), the pump starts with less heat margin. Any additional inefficiency pushes temperatures above safe limits. Fix: use high-temperature seals and bearings, and ensure adequate cooling.
• Insufficient cooling: Many pumps have cooling water jackets on the bearing housing. If the cooling water supply is interrupted or the jacket is scaled, the bearing temperature rises. Fix: verify cooling water flow and clean the jacket if scaled.
• Seal face friction: Dry-running or worn seal faces generate significant heat. The heat transfers to the shaft and bearing housing. Fix: ensure the seal is properly lubricated and in good condition.

Diagnosis

Prevention

• Install a minimum flow bypass line that returns a portion of the discharge to the suction when the main flow is low
• Never run a pump with the discharge valve fully closed
• Monitor bearing temperature continuously — alarm at 80°C, trip at 90°C
• Install cooling water jackets on bearing housings for high-temperature applications
• Ensure adequate ventilation in the pump room — heat builds up in enclosed spaces
• Use high-temperature elastomers and bearing lubricants for hot liquid applications
• Maintain proper lubrication — follow the manufacturer's schedule for grease type and quantity
• Address vibration and cavitation promptly — both generate excess heat