Gas Pressure Washer Maintenance: Oil, Spark Plugs, and Winter Storage

I Learned the Hard Way So You Don’t Have To

I remember the exact moment I killed my first pressure washer. It was a cheap 2700 PSI unit I bought at a garage sale for $80. I ran it for a season, flushed it with water after each use (I thought), and put it in the shed for winter. Come spring, I pulled the cord and got nothing but a sad puff of smoke. The pump was seized. The oil looked like chocolate milk. I spent $150 on a replacement pump that lasted exactly one more season before I cracked the block by forgetting to drain the water.

So yeah, I’ve made the mistakes. The good news? Gas pressure washer maintenance is dead simple if you do three things right: change the oil, swap the spark plug, and store it for winter like it’s a newborn baby. Here’s exactly how I do it now, with every screw-up I made along the way.

Change the Oil: Don’t Skip This, Ever

Most people think “it’s just a little engine on a washer.” They run it for years on the same oil. That’s how you get the chocolate milk I mentioned. Water gets into the crankcase through the pump seal, and old oil doesn’t protect worth a damn.

Tools you need:

• 10mm or 12mm socket wrench (check your manual, but most use one of these)
• Drain pan (I use a $3 aluminum turkey pan from the dollar store)
• Funnel (short, stubby one, not the long skinny kind)
• SAE 30 or 10W-30 oil (I use Briggs & Stratton 10W-30, about $8 a quart)
• Rags. Lots of rags.

Step-by-step:

1. Run the engine for 2-3 minutes. Warm oil flows out faster. I let it idle while I grab the pan and rags. Don’t run it longer or you’ll burn yourself.
2. Disconnect the spark plug wire. Means the engine can’t accidentally start while you’re under it. I’ve seen guys skip this. I’ve been that guy. It’s stupid.
3. Locate the drain plug. Usually on the bottom of the engine block, near the pump. Some washers have a drain hose. Mine has a bolt. Yours probably does too.
4. Put the pan under it and unscrew the plug. Watch out—oil comes out fast. I always end up with a little on the frame. That’s why you have rags.
5. Let it drip for 10 minutes. I use that time to wipe the engine case and check the air filter.
6. Replace the plug, refill with fresh oil. Most engines take about 20 ounces (0.6 quarts). Fill until it reaches the “full” mark on the dipstick. Don’t overfill. I did that once. It smoked like a mosquito fogger for 20 minutes.
7. Reconnect the spark plug wire. Good to go.

Mistake I made: The first time, I used 5W-30 car oil because I had it in the garage. It was too thin. The engine sounded louder and ran hotter. Don’t do that. Small engines need SAE 30 or 10W-30. Spend the $8.

Swap the Spark Plug Every Year

You know that hesitation when you pull the cord and the engine coughs but doesn’t start? That’s often the spark plug. A $4 part that causes a whole afternoon of frustration. I change mine every spring, right after the oil change.

Tools you need:

• New spark plug (check your manual or just take the old one to AutoZone. Usually a Champion RC12YC or similar, about $4)
• Spark plug socket (usually 13/16” or 5/8”. Buy the right one, don’t use pliers)
• Ratchet wrench
• Gap gauge (the little coin-shaped tool. $3 at any auto parts store)

Step-by-step:

1. Pull the spark plug wire off. Grab the boot, not the wire itself. Yanking on the wire will rip it. I’ve done that too. It’s annoying to replace.
2. Clean around the base of the plug. Use a shop rag. You don’t want dirt falling into the cylinder when you pull the plug. I made that mistake once. Had to blow it out with compressed air.
3. Remove the old plug. Turn counterclockwise. It should come out easy. If it’s tight, spray some penetrating oil (like WD-40) around the threads and wait 5 minutes.
4. Check the gap on the new plug. Your owner’s manual will tell you the gap—usually 0.030 inches. Use the gauge to slide it between the electrodes. It should fit snug but not drag. I bend the top electrode gently with a flathead if it’s too tight.
5. Screw it in by hand first. Never use the ratchet to start it. You’ll cross-thread the aluminum head and then you’re really screwed. Turn it with your fingers until it stops, then give it a quarter turn with the wrench.
6. Reattach the wire. Push until you hear it click onto the plug tip.

Winter Storage: The Make-or-Break Step

This is where 90% of pressure washers die. Water freezes inside the pump, expands, and cracks the brass or aluminum housing. I’ve seen it on brand new $600 units. Here’s how I store mine for 5 months of Ohio winter.

Tools you need:

• Pump saver / RV antifreeze (I use the blue stuff that says “non-toxic” and “for RV plumbing,” about $5 a quart)
• Short length of garden hose (3-4 feet is enough)
• Bucket (one gallon or bigger)
• Fuel stabilizer (Sta-Bil, about $8)
• Clean gas can

Step-by-step for the pump:

1. Disconnect the spark plug wire again. Safety first, always.
2. Remove the high-pressure hose and the water inlet hose. Let any leftover water drain out. Tip the washer forward to get the last drops out of the pump.
3. Mix RV antifreeze with water in the bucket. I do a 50/50 mix. Straight antifreeze is fine too, but it’s wasteful.
4. Attach the short garden hose to the water inlet. Put the other end in the bucket of antifreeze mix.
5. Pull the starter cord about 10 times. This sucks the antifreeze into the pump. You’ll see it come out the outlet where the high-pressure hose attaches. Keep pulling until the fluid runs pure blue.
6. Detach the short hose and lay the unit on its side. Let any excess drain out. The pump is now full of antifreeze and won’t crack down to -20°F.

Step-by-step for the engine and fuel system:

1. Add fuel stabilizer to the gas tank. I use about 1 ounce per gallon. Fill the tank to the top with fresh gas. A full tank means less air/condensation inside.
2. Run the engine for 5 minutes. This circulates the treated gas through the carburetor. That’s the whole point—keeps the tiny jets from getting gummed up.
3. Close the fuel valve (if you have one). Run the engine until it dies. This empties the carburetor bowl so old gas doesn’t varnish over winter. If your washer doesn’t have a fuel valve, just run it dry naturally.
4. Change the oil now, not in spring. Old oil is dirty and acidic. It can damage the engine over months of sitting. I do my oil change right before storage.
5. Spray the pump plungers with WD-40 or silicone lube. Prevents rust on the pistons.
6. Cover it with a tarp or old sheet. Not plastic—it traps moisture. A breathable cover keeps dust and spiders out.
7. Store it in a shed or garage. Off the ground, on a pallet or piece of wood. Concrete floors suck moisture into metal parts.

Mistake I made: My second winter, I thought “just draining the pump is enough.” It wasn’t. There was a pocket of water trapped in the bypass valve. It froze and cracked the valve housing. The pump leaked like a sieve in spring. Cost me $100 for a rebuild kit. Now I always use antifreeze. It’s $5 insurance.

Spring Startup: Don’t Just Pull and Pray

When you drag it out in April, don’t just put gas in and yank the cord. Do this:

1. Check the oil level. Top it off if needed.
2. Install the new spark plug. You changed it in fall, right? If not, do it now.
3. Connect the water hose and high-pressure hose. Turn the water on full blast. Hold the spray gun trigger open until water comes out steady. This flushes the antifreeze out of the pump.
4. Start the engine. Let it idle for 2 minutes before you hit the trigger. The pump needs to re-prime.
5. Check for leaks. A few drips from the pump weep hole is normal. A steady stream means the pump seals are shot. Time for a rebuild.

What PSI of gas should I use?

Regular 87 octane is fine. Don’t use ethanol-rich gas if you can avoid it. Ethanol absorbs water and varnishes carbs. I buy ethanol-free gas from the hardware store for about $4/gallon. It costs more but my carburetor never clogs.

Can I use car oil in my pressure washer?

I wouldn’t. Car oil has friction modifiers that small engine clutches don’t need. Stick to SAE 30 or 10W-30 small engine oil. It’s cheap and available at any hardware store.

How do I know if my pump is seized?

Pull the starter cord. If the engine turns over but the pump doesn’t spin (you’ll hear a grinding noise or the engine just stops), the pump is locked. Unplug the spark plug, try to turn the pump shaft with a wrench (on the flywheel side). If it doesn’t budge, it’s seized. Usually from water freezing or old oil turning to sludge.

Is pump saver better than RV antifreeze?

Pump saver is a thick, oily stuff that coats the pistons and displaces water. I’ve used it. It works fine, but it’s $12 a bottle. RV antifreeze is $5 a quart and does the same job. The difference? Pump saver doesn’t freeze and it lubricates the pump seals better. For long-term storage (5+ months), I use pump saver. For a normal winter, antifreeze is fine.

Should I store the pressure washer with a full tank or empty?

Full tank of treated gas. Empty tank means air gets in, condenses water, and rusts the inside of the tank. I learned this the hard way when my tank had a pinhole rust spot after 3 years. Full tank, stabilizer, done.