FrostList

When to Winterize Your Boat in Gilroy, CA

ON TRACK154 days until first 28°F freezeDec 12

In Gilroy, target December 5 to drain, antifreeze, and lay up the boat, about a week before the median first 28°F freeze of December 12; a surprise cold snap is exactly how freeze claims happen. The early-odds date runs roughly 18 days ahead of the median, so build in that buffer.

OUTLOOK

Typical first first 28°F freeze near Dec 12; local deadline about Dec 5. The live 10-day outlook loads here.

Local freeze dates for Gilroy

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Nov 10Nov 27Dec 18
28°F (hard freeze)Nov 24Dec 12Jan 14
24°F (severe)Dec 8Dec 27Jan 19

NOAA station: Gilroy · 0.5 mi away · 194 ft elevation.

Gilroy draws its numbers from Gilroy, 194 feet up and 0.5 miles away. Its median first-freeze dates are 32°F by Nov 27, 28°F by Dec 12, 24°F by Dec 27. The 28°F freeze has come as early as Nov 24 and as late as Jan 14, a 51-day spread. Spring's last 32°F freeze clears around Feb 24.

In Gilroy, freezing nights (32°F) typically begin around Nov 27 and the first hard freeze (28°F) follows near Dec 12. The 32°F date swings from Nov 10 at its earliest to Dec 18 at its latest, near 38 days. The last spring freeze averages Feb 24 and as late as Apr 4, which sets the safe window for reopening outdoor water and de-winterizing gear. Snow barely registers here; the freeze date, around Feb 24, is the one that matters.

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

Gilroy freezes close to Morgan Hill (Dec 12) and about a week ahead of Watsonville (Dec 26) — a reminder that even nearby towns differ by days. Statewide, California prep dates run Jan 9 through Dec 30, which is why Gilroy 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 Gilroy

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

Sprinklers → Dec 2Frozen pipes → Nov 10Car battery → Dec 12Sump pump → Feb 24RV → Dec 2Motorcycle → Nov 27

See the full Gilroy 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 12 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 Gilroy, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.