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Comet P40 Oil Kit
Industrial Pressure Washer Pump Oil
CAT Pump Oil (crankcase)
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How to Choose the Right Pressure Washer Pump Oil
Using the wrong oil is one of the fastest ways to wreck a pump. Detergent motor oils foam under pressure, non-pump-rated oils break down under sustained pressure cycling, and the wrong weight will either starve internal parts or overheat them. The oil follows the pump, never the other way around.
Match the oil to the pump type
Comet P40 diaphragm pumps actually take three different oils: 10w-30 engine oil for the engine, 80w-90 gearbox oil for the gearbox, and 30w non-detergent (AW100) for the pump itself. CAT triplex crankcases run on ISO 68 premium-grade hydraulic oil. General industrial piston pumps use a non-detergent, non-foaming pump oil. Don't mix and match. Gearbox oil is too viscous for a pump crankcase, and detergent oils in any pump will foam and starve the seals.
Why non-detergent matters
Detergent additives in standard motor oil are designed to suspend contaminants so an engine's filter can catch them. Pressure washer pumps don't have that filtration. Detergents foam under high-pressure cycling, which means air pockets in the crankcase, lost lubrication, and eventually seal failure. Every pump oil we sell is non-detergent and non-foaming, formulated specifically for pump duty. The 10w-30 engine oil included in the Comet P40 Oil Kit is a standard detergent oil. That's correct for the engine itself, but it should never go into the pump crankcase.
Stay ahead of the maintenance schedule
Most pump failures aren't from one big event. They're from putting off oil changes. Keep a spare bottle on the truck so you're never tempted to skip a change because the supply house is closed. The Comet P40 Oil Kit includes step-by-step instructions and a free funnel, so a new tech can do the job without a phone call.
Pump Oil Compatibility Chart
| Pump | Recommended oil | Change interval |
|---|---|---|
| Comet P40 (soft wash diaphragm) | Comet P40 Oil Kit (engine, gearbox, pump) | First: 50 hrs / After: 500 hrs (pump) |
| CAT triplex pump crankcase | CAT Pump Oil (ISO 68) | Per CAT pump manual, typically every 250-300 hrs |
| Industrial / general piston pump | Industrial Pressure Washer Pump Oil | First: 50 hrs / After: 150 hrs |
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Frequently Asked Questions
What kind of oil does a pressure washer pump use?
Most pressure washer pumps use a non-detergent, non-foaming oil. Typically 30w (AW100) for diaphragm pumps and ISO 68 hydraulic oil for triplex crankcases. Never use standard motor oil. The detergent additives foam under high-pressure cycling and cause premature seal failure.
How often should I change my pressure washer pump oil?
Change the oil after the first 50 hours of run time on a new pump to flush out break-in debris. After that, change every 150 hours for general industrial pumps and every 500 hours for the Comet P40 pump itself (with engine oil every 100 hours). For CAT triplex crankcases, follow the interval listed in your specific pump manual, typically every 250-300 hours.
Can I use regular motor oil in my pressure washer pump?
No. Motor oil contains detergents that foam under pressure, which causes air pockets, lost lubrication, and accelerated wear. Pump oils are formulated to be non-detergent and non-foaming. The cost difference is small; the cost of a seized pump is not.
What oil does the Comet P40 use?
The Comet P40 sprayer has three components that each take different oils: 10w-30 engine oil for the engine, 80w-90 gearbox oil for the gearbox, and 30w non-detergent (AW100) oil for the pump itself. Our Comet P40 Oil Kit includes all three plus a funnel and step-by-step instructions.
What's the difference between pump oil and engine oil?
Engine oil contains detergents and viscosity modifiers designed for combustion engines. Pump oil is non-detergent, non-foaming, and formulated to stay stable under the constant pressure cycling inside a pump crankcase. They are not interchangeable.
How do I know when my pump oil needs changing?
Pull the dipstick or sight glass and check the color. Clean pump oil is clear to light amber. Milky or cloudy oil means water has gotten into the crankcase (usually from a worn seal). Change it immediately and inspect the seals. Dark or black oil means it's overdue for a change.
