Off-season boat care in Arizona: what to do when you're not on the water

Arizona's two off-seasons

Most of the country winterizes boats in October and de-winterizes in April. Arizona boat owners have two slower periods: mid-June through August when it's too hot, and December through February when the water is cold and the fish aren't biting.

Some people trailer their boats to Rocky Point or California during Arizona summers. Others run Pleasant or Bartlett year-round and don't care about the heat. But most Phoenix boat owners have at least one stretch where the boat sits unused for four to eight weeks.

That idle time is when problems develop. Fuel goes stale, batteries drain, sun cracks vinyl, and rodents move in. This guide covers how to store a boat during Arizona's off-season, whether that's summer or winter.

Fuel system care

Ethanol fuel starts breaking down after 30 days. In Arizona heat, it happens faster. The ethanol separates from the gasoline, absorbs water from humidity, and turns into a gummy mess that clogs carburetors and fuel injectors.

If your boat will sit for more than three weeks, add fuel stabilizer before the last trip. Run the engine for 10 minutes after adding stabilizer so it circulates through the fuel system. This keeps fuel fresh for up to six months.

For longer storage, some people drain the tank completely or run the engine until it's out of gas. That works, but it leaves the fuel system dry, which can cause seals to crack. Stabilized fuel is usually better.

One exception: if you're storing a boat for an entire Arizona summer in an outdoor uncovered space, consider draining the tank. Summer heat accelerates fuel breakdown even with stabilizer, and a full tank in 115-degree heat is a bigger risk than dry seals.

Battery maintenance

Boat batteries drain slowly even when disconnected, and Arizona heat speeds up the process. A fully charged battery left sitting in summer heat will be dead in two months.

Best option: pull the battery and store it indoors on a trickle charger. Garages work if they stay below 90 degrees. If your garage hits 110 in summer, bring the battery inside the house.

If you can't pull the battery, disconnect the negative terminal and check voltage every three weeks. Recharge if it drops below 12.4 volts. A battery that sits discharged for weeks will sulfate and lose capacity permanently.

Lead-acid batteries need a full charge before storage. Lithium batteries should be stored at 50 to 70 percent charge, not fully topped off.

Sun and heat protection

Arizona sun destroys boat interiors faster than saltwater. Vinyl seats crack, carpet fades, and dashboards warp. If your boat sits outside during summer, cover it.

A good boat cover keeps UV off the seats and reduces interior temperatures by 20 degrees. Cheap covers trap heat and moisture, which is worse than no cover. Look for breathable marine canvas with UV treatment and reinforced seams.

Covers need to fit snugly. Loose covers flap in the wind, wear through in weeks, and let dust and sun in through the gaps. If you're storing a boat outside all summer, a custom cover is worth the cost.

Tip: crack a window or install a solar vent if you're covering a boat in summer. Trapped air under a cover can hit 140 degrees and cook the interior.

Rodent prevention

Mice and pack rats move into boats during off-season storage, especially if the boat is covered or in an enclosed trailer. They chew wiring, nest in compartments, and leave droppings everywhere.

Rodent damage isn't covered by most boat insurance policies, and rewiring a boat costs $500 to $2,000 depending on what they chewed.

What works for rodent prevention:

• Close all compartments, including the engine bay and storage hatches
• Remove any food, trash, or fabric (seat cushions, towels, life jackets) that rodents use for nesting
• Place dryer sheets or peppermint oil-soaked cotton balls in enclosed spaces (rodents dislike the smell)
• Check for new droppings or chew marks every two weeks if storing outdoors

Some people use ultrasonic rodent repellers or mothballs. Mothballs work but leave a smell that takes weeks to air out. Ultrasonic devices have mixed results.

Best prevention: store the boat in a climate-controlled unit if possible. Rodents are less likely to move into air-conditioned spaces, and you eliminate heat and sun damage at the same time.

Engine fogging and oil

If your boat will sit for more than two months, consider fogging the engine. Fogging oil coats internal engine parts and prevents rust from forming on cylinder walls and pistons during storage.

How to fog a two-stroke outboard:

1. Run the engine until it's warm
2. Remove the air intake or flame arrestor
3. Spray fogging oil into the carburetor or throttle body while the engine is running
4. Keep spraying until the engine smokes heavily, then shut it off

Four-stroke engines are harder to fog because you need to remove spark plugs and spray directly into the cylinders. Most four-stroke owners skip fogging unless the boat is being stored for a full year.

Change the engine oil before long-term storage, not after. Used oil contains acids and contaminants that corrode engine parts during storage. Fresh oil protects better.

Cooling system flush

Arizona lakes have silt, algae, and mineral buildup that clog engine cooling systems. If you run Lake Pleasant, Bartlett, or Saguaro regularly, flush the cooling system before storing the boat.

For outboards and stern drives with raw-water cooling, connect a garden hose to the flushing port and run fresh water through the system for 10 minutes. This clears out lake water and prevents mineral deposits from hardening inside the cooling passages.

Inboards with closed-cooling systems (freshwater-cooled with a heat exchanger) still need a raw-water flush on the heat exchanger side. Check your owner's manual for the procedure.

Some people add antifreeze to the cooling system for winter storage. Arizona doesn't freeze, so antifreeze isn't needed unless you're storing a boat in Flagstaff or the White Mountains.

Trailer and tire care

Boat trailers suffer during off-season storage. Tires develop flat spots from sitting in one position, bearings seize from lack of use, and brakes rust.

If the boat will sit for more than a month, check tire pressure before storage and add air if needed. Under-inflated tires are more likely to develop flat spots and sidewall cracks.

If storing for a full season, consider putting the trailer on jack stands to take weight off the tires. This prevents flat spots and reduces stress on suspension components.

Trailer bearings need to be greased annually regardless of mileage. If you're storing a boat over winter and the bearings haven't been serviced in a year, repack them before the next launch. Seized bearings are the most common cause of trailer breakdowns on the way to the lake.

Insurance and registration during storage

Arizona boat registration is valid for three years and doesn't require renewal during that period. You can store a boat without re-registering as long as the current registration is still active.

Boat insurance is different. Some policies allow you to reduce coverage to "storage only" during off-season months, which cuts the premium. Storage-only coverage protects against theft, fire, and weather damage but doesn't cover on-water liability or collision.

If you're storing a boat from June through September, call your insurance agent and ask about seasonal coverage adjustment. It can save $200 to $400 per year on a typical policy.

Bringing a boat back from storage

Before launching a boat that's been sitting for weeks or months, do a quick systems check:

• Check battery voltage and recharge if below 12.6 volts
• Inspect bilge for water, oil, or fuel leaks
• Test bilge pump by pouring a gallon of water into the bilge
• Check trailer lights and brakes
• Look for rodent damage in wiring and compartments
• Start the engine on a hose or in a test tank and let it run for five minutes
• Check for cooling water flow from the tell-tale (outboards) or exhaust (inboards)

If the engine won't start after storage, check fuel first. Stale gas is the most common reason boats won't fire after sitting idle. Drain the tank, add fresh fuel, and try again.

For boats stored with fogged engines, expect heavy smoke on the first start. That's normal. The fogging oil burns off after a few minutes of running.

Where to find used boats ready for Arizona storage

If you're shopping for a used boat and plan to store it during summer or winter, ask the seller how the boat was maintained during off-season. Boats that sat uncovered in Arizona sun or were stored with stale fuel and dead batteries often have hidden damage that shows up later.

Check our boats for sale in Phoenix for used inventory. Most listings include service history and storage details. For private-seller boats, see our private seller inspection checklist for what to look for before buying.