How do I winterize a pressure washer?
Drain the water from the hose, gun and pump, then push pump antifreeze through the pump until it comes out the high-pressure port, because water left in a pump can freeze and crack it. On a gas machine, add fuel stabilizer and run it, or drain the fuel for long storage. Store it clean and dry.
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By Kasra Taheri, Founder, LoclisPublished
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Choose the fuel plan
Decide whether the machine will sit two months or less, or longer; the fuel steps differ.[1]
Step 2: Stabilize the fuel or drain it
For short storage, fill the tank, add fuel stabilizer and run the engine for ten minutes; for long storage, drain the tank, fuel lines and carburetor.[1]
Step 3: Change the engine oil
For storage of more than two months, change the engine oil while the engine is completely cool.[1]
Step 4: Oil the cylinder
For long storage, put 0.5 ounces of new oil through the spark plug hole, pull the recoil twice and refit the plug.[1]
Step 5: Drain the hoses
Shut off the water, remove the garden hose, squeeze the trigger to relieve pressure and drain the high-pressure hose.[1]
Step 6: Run pump antifreeze through
Screw the pump protector onto the hose inlet and press the button until it comes out of the high-pressure port.[1]
Step 7: Clean and store
Wipe the machine down, keep water off the engine, and store it clean and dry, out of direct sunlight.[1]
Treat the pump, not just the engine
To winterize a pressure washer, drain the water out of the hose, gun and pump, put an antifreeze and lubricant solution through the pump, and either stabilize or drain the fuel. The pump is the part that freezing destroys. Simpson's manual says leaving water inside the pump during freezing weather will cause severe damage, and that you should always treat the pump with Pump Guard to remove the trapped water and fill it with a lubricating antifreeze solution.[1]
Check your own manual first. The steps below follow Simpson's instructions; other brands use their own pump protector and fuel directions, and the manufacturer's manual wins.
Short winter or long: decide the fuel plan
How long it will sit changes the fuel steps. Simpson separates storage for two months or less (or when freezing temperatures are expected) from storage for more than two months.[1] Note that the shorter plan also covers the case where freezing temperatures are expected, so a machine put away for winter follows it at minimum, with the longer plan added if it will sit past two months.
Alcohol-blended fuels attract moisture, which leads to separation and formation of acids during storage, and acidic fuel and gum deposits can damage the engine's fuel system.[1] Penn State Extension adds that engines that are rarely or seasonally used are especially prone to difficulties with ethanol-blended gasoline.[2] That is why the manual has you either stabilize the fuel or drain it.
Prepare the engine
For storage of two months or less, fill the fuel tank, add a fuel stabilizer per the manufacturer's recommendations, then run the engine for ten minutes so the stabilized fuel circulates through the entire fuel system, squeezing the trigger to keep water flowing through the pump and gun to avoid overheating.[1]
For storage of more than two months, make sure the engine is completely cool, remove all the fuel from the tank, fuel lines and carburetor by loosening the drain screw at the bottom of the carburetor and draining the fuel into an appropriate container, and change the engine oil.[1] The manual then has you remove the spark plug, pour .5 ounces (15 ml) of new oil into the combustion chamber, crank the engine slowly by pulling the recoil twice, and refit the plug.[1]
Drain the water and protect the pump
With the engine off, turn off the water supply and remove the garden hose. Squeeze the trigger to relieve the pressure in the hose and pump, drain the high-pressure hose, then disconnect it from the pump and spray gun.[1] Never leave the hose coiled full of water.
Then comes the pump protector. With Simpson's Pump Guard you screw its adapter into the garden hose inlet on the pump, then press and hold the button until all the water and the Pump Guard starts to come out of the high-pressure port, then unscrew it.[1] The manual recommends using Pump Guard or an equivalent when storing the unit for more than 30 days and when freezing temperatures are expected.[1]
Store it right
Store the pressure washer in a clean, dry area out of direct sunlight.[1] Keep it away from a water heater pilot or other ignition source if any fuel remains in the tank. Clean it with the engine off and cool: Simpson says to use an air compressor set at no more than 25 PSI to clear debris from the surfaces, vents and cooling slots, then wipe the exterior with a damp cloth, and not to wash the engine with a pressure washer or garden hose.[1]
Finally, if you move the machine in a vehicle for storage, turn off the fuel valve, keep it upright and strapped down, and do not leave it in an enclosed space where temperatures can rise, since fuel can vaporize and possibly explode.[1]
Stop and call a pro if
- Water drips from the pump in spring. Simpson's table lists a pump head or tubes damaged from freezing as a cause, and tells owners to contact customer service.[1]
- The machine froze with water in it. Do not start it. A cracked pump head leaks, and the pump may need replacing; see how much pressure washer repair costs in Virginia.
- Fuel system work is beyond you. Simpson recommends that all engine service and repairs be performed by an authorized service center.[1]
- Gas machine will not start in spring. Stale fuel is the usual reason; a gummed carburetor is a shop job.
Getting help in Virginia
In spring, if the machine will not hold pressure, read how to fix a pressure washer that will not build pressure, and if it pulses, see why a pressure washer pulses. Before paying for pump work, weigh whether a pressure washer is worth repairing. You can also browse small engine repair answers or find local small engine shops.
When you are ready, describe the machine and local shops can quote it.
Common questions
- Do I really need pump antifreeze?
- If it could freeze where you store it, yes. Simpson says leaving water inside the pump during freezing weather will cause severe damage, and that the pump should be treated with Pump Guard to remove trapped water and fill it with a lubricating antifreeze solution. Draining the hose alone does not empty the pump.
- Can I use car antifreeze in the pump?
- Follow your manual. Simpson recommends its Pump Guard or an equivalent product made for pressure washer pumps, and says nothing about automotive coolant. Use a product the pump maker approves, because some fluids can harm the seals.
- Should I leave gas in the tank over winter?
- Only with a stabilizer, and only for shorter storage. Simpson's plan for storage over two months is to drain the tank, fuel lines and carburetor instead. Alcohol-blended fuel attracts moisture and forms acids and gum in storage.
- Does an electric pressure washer need winterizing too?
- Yes, the pump part. There is no fuel to deal with, but the pump, hose and gun can hold water that freezes. Drain them, run pump protector through the pump and store the unit indoors, after unplugging it.
- What if I stored it with water inside and it froze?
- Do not start it. Simpson lists a pump head or tubes damaged from freezing as a cause of water leaking at the pump and says to contact customer service. A cracked pump head usually means a pump replacement.
Sources
- [1] Pressure Washer Use and Care Manual (part 7110656NOCA, rev. B, February 2026), Simpson Cleaning (FNA Group). Checked October 28, 2026.
- [2] Fuel Ethanol: Hero or Villain?, Penn State Extension. Checked October 28, 2026.
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