FrostList

When to Winterize Your Boat in Merced, CA

ON TRACK153 days until first 28°F freezeDec 11

Plan to haul out and winterize your boat in Merced by December 4. The first 28°F freeze near Merced averages December 11 in the 1991–2020 normals, and freeze damage often surprises owners in milder states. Plan for the early end: the one-in-ten date lands about 19 days before the median.

OUTLOOK

Typical first first 28°F freeze near Dec 11; local deadline about Dec 4. The live 10-day outlook loads here.

Local freeze dates for Merced

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 5Nov 24Dec 14
28°F (hard freeze)Nov 22Dec 11Jan 14
24°F (severe)Dec 2Dec 24Jan 24

NOAA station: Merced · 2.0 mi away · 154 ft elevation.

Numbers for Merced come from Merced, 2.0 miles away at 154 feet, where the medians fall 32°F by Nov 24, 28°F by Dec 11, 24°F by Dec 24. Year to year the 28°F date has ranged from Nov 22 to Jan 14 — about 53 days apart. Spring's last 32°F freeze clears around Mar 3.

Expect the first frost near Nov 24 in Merced and the first hard freeze by about Dec 11. That first freezing night has ranged from Nov 5 to Dec 14, roughly a 39-day spread. On the spring side, the last 32°F freeze clears around Mar 3 and as late as Apr 10 — the green light for reopening water and de-winterizing. With almost no snow in a normal year, cold — not plowing — sets the calendar, and it centers on Mar 3.

Your boat checklist

  1. Change the engine oil and filter while the motor is warm so contaminants leave with the old oil.
  2. Run the engine on antifreeze until pink fluid reaches the outlet, protecting the block and manifolds.
    Helpful gear: Marine antifreeze — Recommended pick
  3. Fog the cylinders with fogging oil as the engine runs down to coat internal parts against corrosion.
    Helpful gear: Fogging oil — Recommended pick
  4. Top off the fuel tank and add stabilizer to limit condensation and protect ethanol-blend fuel.
    Helpful gear: Marine fuel stabilizer — Recommended pick
  5. Drain the raw-water system, the livewell, and any washdown lines that can trap water.
  6. Remove the battery, charge it fully, and keep it on a maintainer over the layup.
    Helpful gear: Battery maintainer — Recommended pick
  7. Support the cover so snow and rain shed off, and leave vents so the interior can breathe.
  8. For an inboard or sterndrive, follow the manual closely — those blocks are the ones freeze claims hit hardest.

What to have on hand

Marine antifreeze
Propylene-glycol fluid rated for engine blocks and systems.
Recommended pick
Marine fuel stabilizer
Additive that protects ethanol-blend fuel over the layup.
Recommended pick
Fogging oil
Spray that coats cylinders against corrosion in storage.
Recommended pick
Battery maintainer
Keeps the cranking battery topped off on the trailer.
Recommended pick

What this means locally

Compared with nearby cities, Merced's first-freeze date near Dec 11 sits about a week ahead of Turlock (Dec 24) and about a week ahead of Ceres (Dec 21). California's deadlines span Jan 9 to Dec 30 statewide — one date for all of California would be off by weeks for Merced. Once you know Merced's freeze date, use it to winterize an RV and store a motorcycle too.

Other winter jobs in Merced

Every task below is dated to Merced's own freeze and snow normals.

Sprinklers → Dec 1Frozen pipes → Nov 5Car battery → Dec 11Sump pump → Mar 3RV → Dec 1Motorcycle → Nov 24

See the full Merced winter checklist, in order →

Frequently asked questions

At what temperature does a boat engine block crack?
Trapped water in an engine block or manifold can freeze and crack the casting once temperatures fall below 32°F and stay there long enough. Inboard and sterndrive blocks hold the most water and are the most vulnerable. Draining fully and adding antifreeze before the first hard freeze near Dec 11 is the protection.
Do outboards need winterizing?
Yes. An outboard should be drained so no water sits in the powerhead or lower unit, and the fuel system stabilized. Outboards self-drain better than inboards when tilted down, but fogging the cylinders and changing the gear oil are still part of a proper layup.
Fogging oil: is it necessary?
Fogging coats the cylinder walls and internal parts with a film that resists corrosion during months of storage. On engines that sit all winter it is cheap insurance against rust, especially in humid or coastal storage. Follow your engine maker's guidance on how to apply it.
How much does boat winterization cost?
A professional winterization varies with engine type and boat size, and inboards cost more than a simple outboard. Doing it yourself costs mainly antifreeze, oil, and fogging oil. Either way, the bill is far smaller than repairing a cracked block, which is the failure winterizing prevents.
Do boats in CA really need winterizing?
If temperatures reach freezing where the boat is stored, yes. Freeze claims are common in milder states precisely because owners assume they are safe and skip the step, then a rare cold snap cracks a block. Check the local freeze dates above and protect the engine before the first hard freeze.
When should I de-winterize my boat?
De-winterize in spring once the risk of a hard freeze has passed for your area. Reconnect and charge the battery, replace drain plugs, check hoses and clamps, and inspect the fuel system before the first launch. Reopening too early leaves the block exposed to a late cold snap.

Data: NOAA 1991–2020 normals via Merced, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.