Plenty of dealerships will tell you winterization is too complicated to attempt on your own. That’s not quite true.

Some of it is genuinely straightforward and worth doing yourself. Some of it will cost you an engine if you get it wrong. The useful thing is knowing which is which — so here’s an honest breakdown, split into what a reasonably handy owner can handle and what we’d recommend leaving to a certified technician.

What You Can Reasonably Do Yourself

Clean the Boat Thoroughly

Wash the hull, scrub the waterline, and get any growth or staining off before it sits for months. Vacuum the interior, wipe down all vinyl, and clean out every compartment. Food wrappers, damp towels, and forgotten tackle turn into mildew and attract pests over a winter.

Dry Everything Out

Pull every cushion, life jacket, rope, and towel out of the boat and store them somewhere dry. Leave compartments and the head propped open so air can move. Moisture with no ventilation is how you get a boat that smells like a basement in April.

Remove Valuables and Electronics

Portable GPS units, fish finders that unclip, stereo faceplates, tools, and anything else worth stealing should come out. Cold and condensation aren’t good for electronics either.

Top Off the Fuel Tank

A full tank leaves less room for air, which means less condensation forming inside the tank over the winter. Fill it before storage rather than leaving it a quarter full.

Add Fuel Stabilizer

Add stabilizer to the full tank, then run the engine a few minutes so treated fuel makes it through the entire fuel system — not just the tank. Untreated ethanol fuel sitting for months is a leading cause of spring no-start calls.

Pull and Store the Batteries

Disconnect the batteries, take them out, and store them somewhere that doesn’t freeze. Put them on a maintainer through the winter. A battery left discharged in a cold boat is frequently a battery you’re replacing in March.

Cover It Properly

Use a cover that actually fits and allows ventilation. A cheap tarp cinched down tight traps moisture and does more harm than leaving it uncovered. If the boat is outside, support the cover so water and ice can’t pool in the middle.

Check the Trailer

Inflate the tires, check for cracking, inspect the lights, and grease the bearings. Trailers get ignored all winter and then fail on the way to the ramp in spring.

What You Should Leave to a Technician

Draining the Cooling System

This is the one that matters most and the one most commonly done incompletely. On a sterndrive or inboard, water sits in the block, manifolds, and cooling passages — and missing a single drain point can crack a block. Every engine has its own drain locations and its own procedure. A technician who works on your specific engine knows where all of them are.

Antifreeze and Fogging

Running the correct marine antifreeze through the cooling system and fogging the cylinders to protect against internal corrosion both require doing it in the right order with the right products. Automotive antifreeze is not the same thing, and using the wrong product causes its own problems.

Lower Unit Service

Draining and refilling the lower unit gear oil is also a diagnostic step — what comes out tells a technician whether water is getting in past the seals. Milky oil means a seal problem that needs addressing before spring, not after.

Engine Oil and Filter Change

Used oil holds acids and combustion byproducts. Leaving it in the engine all winter lets those sit against internal components for months. Fall is the right time to change it, and it’s typically done as part of winterization anyway.

Anything Warranty-Related

If your boat is under factory warranty, having winterization done and documented by a certified dealer protects you. Freeze damage is generally considered preventable and is often excluded from warranty coverage. A documented service record from a certified technician is the cleanest possible answer if a question ever comes up.

The Honest Cost Comparison

DIY winterization saves you the labor charge. What it costs you is time, the risk of missing a drain point, and the loss of having a trained set of eyes on the boat before it sits for five months.

Our view, for what it’s worth: the cleaning, drying, fuel treatment, battery, and cover work are all genuinely worth doing yourself. The engine and cooling system work is where the downside risk is severe enough that professional service is the better economics — one cracked block costs more than a decade of winterization service.

The Short Version

Do yourself: clean and dry the boat, remove gear and valuables, top off fuel, add stabilizer and run it through, pull and maintain the batteries, cover it properly, service the trailer.

Leave to a tech: cooling system drain, antifreeze, fogging, lower unit service, oil and filter change, and anything touching warranty.

Book Winterization at Nichols Marine

Our certified service technicians hold credentials from Mercury Outboard, MerCruiser, Yamaha, Ilmor, and Volvo Penta, and we service all makes — not just boats purchased from us.

Schedule at your nearest location: Tulsa, Norman, McAlester, Monkey Island, Shangri La Marina, Longview, or Lewisville.

Not sure when to schedule? Our guide on when to winterize in Oklahoma and Texas breaks down the timing by region. Still figuring out where the boat goes afterward? See indoor vs. outdoor boat storage.

Have other ownership questions? Our boat buying and ownership FAQ covers service, financing, trade-ins, and more.