FrostList

When to Winterize Your Boat in San Leandro, CA

ON TRACK170 days until first 28°F freezeDec 28

Freeze protection for a San Leandro boat keys off the first 28°F freeze, which averages December 28, so haul out and winterize by December 21 to beat it. It's a short step from frost to a hard freeze: roughly 5 days on average.

OUTLOOK

Typical first first 28°F freeze near Dec 28; local deadline about Dec 21. The live 10-day outlook loads here.

Local freeze dates for San Leandro

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 30Dec 23Jan 24
28°F (hard freeze)Dec 6Dec 28Jan 12

NOAA station: Oakland Metro Intl AP · 3.5 mi away · 6 ft elevation.

The reference station for San Leandro is Oakland Metro Intl AP (3.5 mi, 6 ft). First freeze there: 32°F by Dec 23, 28°F by Dec 28. The 28°F freeze has come as early as Dec 6 and as late as Jan 12, a 37-day spread. Spring's last 32°F freeze clears around Jan 7.

Expect the first frost near Dec 23 in San Leandro and the first hard freeze by about Dec 28. Year to year, the first 32°F night has fallen anywhere from Nov 30 to Jan 24 — about 55 days apart. Spring's final freeze lands near Jan 7 and as late as Feb 8, so that is when outdoor water and stored gear can safely come back online. Measurable snow is rare, so the freeze near Jan 7 — not snow load — drives the local prep list.

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

San Leandro freezes close to Alameda (Dec 28) and later than San Ramon (Jan 16) — a reminder that even nearby towns differ by days. Statewide, California prep dates run Jan 9 through Dec 30, which is why San Leandro gets its own number rather than a California-wide average. The same freeze also decides when to winterize an RV and store a motorcycle.

Other winter jobs in San Leandro

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

Sprinklers → Dec 18Frozen pipes → Nov 30Car battery → Dec 28Sump pump → Jan 7RV → Dec 18Motorcycle → Dec 23

See the full San Leandro 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 28 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 Oakland Metro Intl AP, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.