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De-winterizing your boat is all about timing, thorough checks, and smart safety habits. Once night-time temperatures stay consistently above freezing, walk through a proven 10-point inspection, and run a controlled on-land test before you hit the water. A few hours and $50-$100 in supplies for spring commissioning could save you from a cracked engine block and a major repair bill later. Follow the step-by-step plan below and you’ll start the season with confidence.
Why Spring Readiness Matters
When water is left inside an engine over the colder months, it expands as it freezes, creating pressure that can split cast-iron blocks and plastic hoses, damage the raw-water pump, and punch pinholes in heat-exchanger tubes. To make matters worse, most basic boat-insurance policies don’t cover freeze damage. A little preparation now means more days on the water and fewer repairs.
Step-by-Step: Bring Your Engine Back to Life
Outboards, inboards, and sterndrives all share the same core jobs. Follow the steps below so you don’t miss anything.
1. Clean & Inspect
Pull back the cover or cowling and give every surface a wipe-down. A clean engine makes it easier to spot cracks, rodent nests, and fuel leaks. While you’re at it, give the hull and trailer a thorough once-over too.
2. Change the Oil
Run the engine on a hose just long enough to warm it, then drain the oil and replace the filter. Warm oil flows faster and carries out gritty sludge that can scar bearings. If you boat in salt water, add a corrosion-inhibiting additive for extra protection.
3. Refresh the Cooling System
Replace any hose that feels brittle or shows bulges. Empty sea-strainer bowls, then flush the block if you skipped it last fall. Refill closed-loop systems with a 50/50 mix of coolant and distilled water.
4. Service the Battery
Disconnect the trickle charger, top off each cell with distilled water, and clean the terminals. Use a multimeter to confirm at least 12.6 volts. A weak battery is the #1 reason spring engines won’t crank.
5. Tune the Ignition
On gas inboards, lift the distributor cap and scrub off any green fuzz. Tiny air gaps invite misfires at high RPM, so make sure to tighten the cap evenly.
6. Refresh the Fuel System
If you forgot stabilizer last fall, drain stale gas and change the water-separating filter. Squeeze the primer bulb until it’s hard, then inspect the fuel vent; a blocked vent can collapse a tank under suction.
7. Check Belts & Hoses
Press the belt halfway between pulleys, if you see more than half an inch of slack or a trail of black dust, it’s time to replace it. Squeeze your cooling hoses too – if they feel soft, swap them out now. Replacing parts dockside is far cheaper than calling for a tow.
8. Test Electronics & Pumps
Power up the GPS, VHF, depth finder, and bilge pump. Lift the float switch by hand to make sure it works. If it’s stuck, you can fix it in minutes instead of risking your boat mid-season.
9. Spin the Prop & Change Gear Oil (Outboards)
Drain the lower-unit gear lube and check its condition. Milky fluid signals water intrusion and the need for new seals. Remove the prop, clear away any fishing line and grease to the prop shaft before reassembly.
10. Run It on the Hose
Clamp flushing muffs (outboards) or a fake-a-lake (inboards) over the water inlets, then fire up the engine. Let it warm to operating temp while you watch for a steady telltale stream (or exhaust water) and stable gauge readings.
Outboard Extras
- Replace the water-pump impeller and thermostat every 200 hours.
- Inspect rubber bellows, steering cables, and trim-tilt fluid.
- Swap sacrificial anodes when they’re half gone.
Inboard & Sterndrive Extras
- Confirm every block drain plug is back in.
- Use a mirror to spot leaks around manifolds on first start-up.
- Test that the shift cables move smoothly in and out of gear. Sticky or binding cables can quickly destroy a gearbox.
Beyond the Engine: Whole-Boat Checks
Freshwater & Sanitation
Pump pink antifreeze out of all faucets and the head, then refill tanks with potable water. Add treatment to the holding tank to keep odors under control.
HVAC
Run the air-conditioning pump until pink antifreeze is fully cleared and freshwater flows. Once clear, reconnect the seawater intake hose.
Safety Gear Refresher
Inspect all life jackets, flares, fire extinguishers, and sound-signaling devices. Replace any expired or damaged items now before the launch rush makes gear harder to find.
Pitfalls That Ruin Launch Day
- Forgetting the transom plug. Tape it to your car keys the night before so you don’t forget it.
- Overfilling the fuel tank. Warm fuel expands and can gush out the vent, creating a mess and fire risk
- Ignoring a dinged prop. Even a small bend or curl can throw the driveline out of balance and cause major damage.
- Skipping a solo shakedown. Take the boat out alone for about twenty minutes before inviting guests. It’s the easiest way to spot and fix issues without an audience.
Launch-Day Playbook
- At Home: Warm the engine on the hose. Check gauges and look for drips.
- Ramp Prep: Back in, leave the bow strap on, start the engine, and verify oil pressure and cooling water.
- On the Water: Idle out, run mid-throttle for 15 minutes, then open the engine box for one final leak check.
When to Call in the Pros
- You spot milky gear oil or a hairline block crack.
- The engine overheats within seconds of start-up.
- Electrical gremlins keep blowing fuses.
Professional yards typically charge $150–$500 for a basic de-winterize on a runabout but expect more for cruisers. Major repairs, however, can easily climb into the thousands.
Why Sea Tow® Belongs on Your Spring Checklist
Even the best-maintained boats have off days. Sea Tow membership gives you a 24/7 direct connection to your local Captain, unlimited towing in your home area, and priority service. You never know when the unexpected will happen.
Ready, Set, Splash!
Spring commissioning isn’t glamorous, but it pays you back with every trouble-free hour on the water. Follow the checklist, keep an eye on the forecast, and recycle your fluids responsibly. Do that and you’ll hit the throttle on opening day knowing your engine and your crew are good to go.
And if you happen to get stuck? Call 800-4-SEATOW or tap the Sea Tow app any time, day or night.
Sea Tow Team
Sea Tow has been the premier leader in on-water boating assistance since 1983. We want to share news, press, tips and all things boating.