Reciprocating compressors are air-cooled -- the cooling fins on the cylinder and head rely on airflow to dissipate heat. Put the compressor in a closet, corner, or enclosed space without adequate ventilation and it will overheat. The most common and easiest-to-fix cause of overheating.

What you'll see

The compressor runs hot -- the head and cylinder are too hot to touch, the thermal overload trips, or the machine shuts down on high temperature. It often works fine in the morning (cooler ambient) and starts overheating in the afternoon. Moving the compressor to a different location temporarily fixes the problem. The compressor may have been in its current location for years and only recently started overheating -- because surrounding equipment or storage was added that blocks airflow.
Before you assume this is the problem

If the compressor is in a well-ventilated space with good airflow and still overheats, the problem is internal -- valve damage, head gasket, or excessive duty cycle. See: Leaking Valves, Blown Head Gasket, Excessive Duty Cycle.

See all causes of overheating / high cylinder temperature →

How to diagnose

  1. Assess the compressor location

    Look at the environment: Is the compressor in a closet, under a bench, or in a tight corner? Is there at least 30cm (12 inches) of clearance on all sides? Are there obstructions blocking airflow to the cooling fins? Is hot exhaust air recirculating back to the intake? Is the room temperature above 40C (104F)?
    Result: Enclosed, cramped, or hot = ventilation problem. Open, clear airflow = look elsewhere.

  2. Test in a different location

    If possible, temporarily move the compressor to an open, well-ventilated area and run it. If the overheating problem goes away, the original location was the issue. This is the definitive test.
    Result: Problem goes away in open space = original location is the cause.

How to fix it

  1. Improve the location

    Move the compressor to a cooler, better-ventilated space. Ensure at least 30cm clearance around the pump and motor for airflow. If it must stay in its current location, add ventilation: install an exhaust fan to pull hot air out of the room, or duct fresh air to the compressor's intake area. Make sure the cooling fins have an unobstructed path for air to flow across them.

  2. Consider ducting for enclosed rooms

    If the compressor must be in an enclosed room (noise reasons), install fresh air intake and hot air exhaust ducts. The exhaust should be at the ceiling (hot air rises). The intake should be low on the opposite wall. The airflow volume should be at least 10 times the compressor's CFM to carry away the heat. An exhaust fan sized to the room is the simplest solution.

Common mistakes

Don't build an enclosure around the compressor for noise reduction without providing ventilation. I've seen beautiful sound-deadening enclosures that cook the compressor in 10 minutes. The enclosure needs air in and air out -- and enough volume to actually cool the machine. Also: don't point the compressor's hot exhaust air at a wall and expect it to work. The hot air bounces back and gets re-ingested. Aim the exhaust toward the room exit or exhaust duct.

Parts & tools

Exhaust fan (if adding ventilation). Ducting materials. Thermometer to check ambient temperature. No compressor parts needed -- this is an installation/environment issue.

Review safety precautions before starting →

Safety

An overheating compressor has scalding surfaces. Don't move it while hot. Wait for cool-down. Ensure the new location has adequate clearance before restarting.