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Winterizing a pressure washer takes about ten minutes and prevents the single most common way these machines die. Disconnect the water, run the residual pressure out, drain the hose and pump, inject a few ounces of pump saver antifreeze, and — on a gas machine — treat or drain the fuel. Water expands roughly 9% as it freezes, and the ounce or two trapped in a pump has nowhere to go, so it cracks the housing or splits a seal. The machine looks perfect in April and will not build pressure.
This is not a maintenance nicety. Across the ownership record for every brand, "lost pressure over the winter" is one of the two or three most common complaints, and it is nearly always a pump that was put away wet.
When to do it
Before the first hard freeze where the machine will be stored, not after. A garage or unheated shed tracks outdoor temperature closely, so a single overnight dip below 32°F is enough. In practice that means:
| USDA zone / region | Typical first hard freeze | Winterize by |
|---|---|---|
| Zones 3–4 (Upper Midwest, N. New England) | Late September | Mid-September |
| Zone 5 (Great Lakes, Mountain West) | Mid-October | Early October |
| Zone 6 (Mid-Atlantic, Ohio Valley) | Late October | Mid-October |
| Zone 7 (Piedmont, mid-South, Pacific NW) | Early November | Late October |
| Zones 8–9 (Deep South, Texas, coastal CA) | December, or a cold snap | Before any freeze warning |
| Zone 10+ (S. Florida, S. Texas, Hawaii) | Rarely freezes | Drain only; no antifreeze needed |
The zone 8–9 case is the one that catches people out. A machine that lives outdoors in Houston or Atlanta is fine for years and then meets one hard freeze event, and the pump cracks in a single night. If a freeze warning is issued and the washer is not winterized, bringing it indoors for the night is a perfectly good substitute.
Tools and materials
- Pump saver antifreeze — a 4 oz can does one machine. STA-BIL Pump Protector (paid link) and Briggs & Stratton 6151 Pump Saver (paid link) are the two most-owned; both are propylene glycol with a lubricant package.
- Fuel stabilizer (gas machines only) — or a plan to run the tank dry.
- Fresh pump oil and engine oil if your machine has serviceable sumps. See how to change pressure washer oil.
- A funnel, a rag, a bucket, and a garden hose.
Cordless and hose-fed portable washers still have a pump; they still need draining. Machines with a genuinely sealed maintenance-free pump still hold water in the head and still crack.
The ten-minute procedure
- Run the machine clean. If you have used detergent, run clear water through the soap line for a minute so nothing is left sitting in the injector all winter. Dried detergent gums up the chemical injector and is a common spring complaint.
- Shut off the water supply, then bleed the pressure. Turn off the tap first, then — with the machine off — squeeze the trigger until no more water comes out. There is trapped pressure in the hose and gun even after shutdown, and this is the step people skip. Never disconnect a fitting under pressure.
- Disconnect and drain the hoses. Pull both the garden hose and the high-pressure hose. Walk the high-pressure hose out straight, then coil it from one end so the water runs out. Store it loosely coiled — tight coils in cold weather set kinks that become weak points.
- Drain the gun, wand and nozzles. Squeeze the trigger with the gun pointed down. Pull the nozzle tips out of the quick-connect and store them somewhere you will find them; a nozzle left in the coupler with water behind the o-ring is a small freeze risk of its own.
- Empty the detergent tanks. Tip them out and rinse. Detergent left in an onboard tank separates and stains, and some formulations attack the tank seals.
- Purge the pump. With everything disconnected, run the machine for no more than five seconds to push residual water out of the pump. Do not run it dry for longer — a pressure washer pump is water-lubricated and running dry damages the seals it is designed to protect.
- Inject pump saver. Screw or press the can onto the pump's water inlet (the garden hose connection) and squeeze until you see the antifreeze — usually pink or blue — come out of the pump outlet. That tells you it has displaced the water all the way through. Some cans instruct you to pull the recoil starter or briefly bump the motor to circulate it; follow the can, not a video.
- Gas machines: deal with the fuel. Either add stabilizer to a full tank and run the engine five minutes so treated fuel reaches the carburetor, or shut off the fuel valve and run the engine until it dies. Do not leave a half tank of untreated gasoline. Change the engine oil now rather than in spring.
- Store it off the concrete. A pallet, shelf or two boards is enough. Concrete floors are colder than the air above them and wick moisture into everything sitting on them. Cover loosely so condensation can escape.
Bringing it back in spring
The antifreeze must come out before you clean anything with it. Connect the garden hose, point the outlet away from the lawn and into a bucket or a drain that goes to the sewer rather than to a storm drain, and run water through for thirty seconds until it runs clear. Propylene glycol is far less toxic than automotive coolant, but it is still not something to flush across a lawn or into a waterway — the EPA's stormwater program treats storm drains as a direct route to surface water, and many municipal ordinances follow suit.
Then check the pump oil level if the pump has a sight glass, check the inlet screen for grit, reconnect, and purge the air before pulling the trigger under load: run water through the machine with the trigger held and the power off until the flow is steady and free of sputtering. Starting a pump full of air is a small but avoidable way to damage it.
The mistakes that cost pumps
Draining but not adding antifreeze. Draining removes most of the water, not all of it. Water sits in the valve pockets, the unloader and the chemical injector. This is the failure mode owners are most surprised by, because they did winterize — partly.
Running the pump dry to "blow it out". Five seconds is fine. Thirty seconds cooks the seals. The pump relies on water for both lubrication and cooling.
Leaving the high-pressure hose coiled tight in the cold. Rubber and PVC stiffen below freezing and take a set. The kink becomes a weak spot that bursts under pressure the following summer.
Automotive antifreeze. Ethylene glycol is sweet-tasting and toxic to pets and wildlife, and it ends up on your driveway in spring. Use the propylene-glycol product sold for the job.
Storing gas with untreated fuel. Ethanol-blended pump gasoline absorbs water and separates over months, and the residue varnishes the carburetor jets. This is the single most common reason a gas pressure washer will not start in April.
One safety note that applies year-round
Bleed the pressure before disconnecting anything. Trapped pressure in a hose or gun releases suddenly when a fitting is loosened, and a high-pressure stream can penetrate skin. A high-pressure injection injury looks like a small puncture and is a surgical emergency — the visible wound badly understates the internal damage. A 2023 analysis of a decade of US emergency-department data in the journal Hand found pressure washers accounted for around 90% of high-pressure injection hand injuries. If a jet breaks your skin, go to an emergency department and say explicitly that it was a pressure washer injection injury. More: pressure washer injection injuries.
Never run a gas pressure washer indoors, in a garage or on a covered porch, including while winterizing. Carbon monoxide from a small engine reaches lethal concentrations in an enclosed space quickly.
Where to go next
If your pump did not survive last winter, replacement pumps are often cheaper than a new machine on gas units and rarely worth it on cheap electrics. For general off-season storage see how to store a pressure washer, and for pressure problems that are not freeze damage see why a pressure washer loses pressure. Shopping for a replacement? Start at the best pressure washers.
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