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Pressure Washer Pump Oil: What Type and How Often, by Pump Brand

Updated 2026-10-29 · Written and checked by the Manual Matters team against the manufacturer documents listed under Sources.

Short answer: a gas pressure washer has two separate oil reservoirs, the engine crankcase and the pump crankcase, and they usually take different oil. Pump manufacturers disagree on both the oil and the interval: Cat Pumps requires its own ISO 68 pump oil, changed after the first 50 hours and then every 500 hours; the Champion 100386 manual calls for non-detergent SAE 30 (or Champion's pump oil), first at 50 hours and then every 250; Simpson's manual for AAA pumps specifies Simpson pump oil or SAE 15W-40, first at 50 hours and then every 100 hours or 3 months. Use your pump's manual.

Table of pressure washer pump oil type and change intervals for Cat Pumps, Champion and Simpson
Table of pressure washer pump oil type and change intervals for Cat Pumps, Champion and Simpson

Some consumer pumps have no serviceable oil reservoir; if your manual lists no pump oil service, there is nothing to change. Check for a dipstick, fill cap, or sight glass on the pump.

Pump oil by manufacturer

Pump / manualOil specifiedFirst changeThen every
Cat PumpsCat Pumps ISO 68 pump oil only (no alternatives)50 hours500 hours
Champion 100386Champion AR64516 pump oil, or non-detergent SAE 3050 hours250 hours
Simpson (AAA pump)Simpson pump oil or SAE 15W-4050 hours100 hours or 3 months
Simpson (CAT pump)Non-detergent ISO 68 pump oilPer manualPer manual

How to change pump oil

  1. Shut off the engine, let everything cool, and disconnect the spark plug wire.
  2. Relieve water pressure by squeezing the spray gun trigger, then disconnect hoses.
  3. Place a pan under the pump drain plug and remove the fill cap, then the drain plug.
  4. Let the oil drain completely. Inspect it: Cat Pumps says milky oil indicates worn seals letting water into the crankcase.
  5. Reinstall the drain plug.
  6. Refill with the oil your manual specifies. On pumps with a bubble or sight gauge, Cat Pumps says to fill to the center of the gauge.
  7. Reinstall the fill cap and check for leaks on first run.

Don't forget the engine and the freeze risk

The engine has its own schedule. The Champion 100386 engine takes 10W-30, up to 1.2 quarts. Engine care for Briggs and Honda engines is covered in the Briggs maintenance schedule and the Honda GCV guide.

Simpson's manual says to use pump antifreeze or a pump-protector product when storing more than 30 days or when freezing temperatures are expected. Water left in a pump that freezes can crack it. For the engine's fuel, see Run it dry or stabilize it?.

Diagram of the separate engine and pump oil reservoirs on a gas pressure washer
Diagram of the separate engine and pump oil reservoirs on a gas pressure washer

FAQ

Can I use engine oil in a pressure washer pump?

Only if your pump's manual allows it. Simpson's AAA-pump manual allows SAE 15W-40, Champion's allows non-detergent SAE 30, and Cat Pumps says to use only its own pump oil.

What does milky pump oil mean?

Cat Pumps says it indicates water in the oil from worn seals. Change the oil and have the seals inspected.

My pump has no dipstick. Do I still need to change the oil?

Some pumps are not designed for oil service. If your manual lists no pump oil service, there is nothing to change.

How full should the pump be?

On Cat Pumps with a bubble gauge, fill to the center of the gauge. Otherwise use the level your manual gives.

Sources