Share of freeze-damage insurance claims involving a cracked engine block or exhaust manifolds, per a 10-year analysis of BoatUS claim files.
BoatUSWhen to Winterize Your Boat in San Antonio, TX
ON TRACK157 days until first 28°F freezeDec 15
In San Antonio, target December 8 to drain, antifreeze, and lay up the boat, about a week before the median first 28°F freeze of December 15; a surprise cold snap is exactly how freeze claims happen. Plan for the early end: the one-in-ten date lands about 26 days before the median.
Dec 8Local deadline
Dec 15Median first 28°F
62 days28°F window spread
0 inSnow per season
OUTLOOK
Typical first first 28°F freeze near Dec 15; local deadline about Dec 8. The live 10-day outlook loads here.
Local freeze dates for San Antonio
| Threshold | Early (1-in-10) | Median | Late (9-in-10) |
|---|---|---|---|
| 32°F (light freeze) | Nov 7 | Nov 28 | Dec 21 |
| 28°F (hard freeze) | Nov 19 | Dec 15 | Jan 20 |
| 24°F (severe) | Dec 3 | Jan 1 | Feb 4 |
Bars span the early (1-in-10) to late (9-in-10) window for each freeze threshold; the dot marks the median year. The dashed line is the local prep deadline.
NOAA station: San Antonio Incarnate Word · 3.4 mi away · 700 ft elevation.
- Hard freezes are rare and late in San Antonio, which is exactly why they catch people off guard when they do come.
- The 62-day gap between the earliest and latest freeze dates here is wide, so the live outlook matters more than the calendar.
San Antonio draws its numbers from San Antonio Incarnate Word, 700 feet up and 3.4 miles away. Its median first-freeze dates are 32°F by Nov 28, 28°F by Dec 15, 24°F by Jan 1. That hard freeze has landed anywhere from Nov 19 to Jan 20, a swing of roughly 62 days. Spring's last 32°F freeze clears around Feb 25. Snowfall averages 0 inches a year.
Expect the first frost near Nov 28 in San Antonio and the first hard freeze by about Dec 15. That first freezing night has ranged from Nov 7 to Dec 21, roughly a 44-day spread. On the spring side, the last 32°F freeze clears around Feb 25 and as late as Mar 19 — 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 Feb 25.
Your boat checklist
- Change the engine oil and filter while the motor is warm so contaminants leave with the old oil.
- Run the engine on antifreeze until pink fluid reaches the outlet, protecting the block and manifolds.Helpful gear: Marine antifreeze — Recommended pick
- Fog the cylinders with fogging oil as the engine runs down to coat internal parts against corrosion.Helpful gear: Fogging oil — Recommended pick
- Top off the fuel tank and add stabilizer to limit condensation and protect ethanol-blend fuel.Helpful gear: Marine fuel stabilizer — Recommended pick
- Drain the raw-water system, the livewell, and any washdown lines that can trap water.
- Remove the battery, charge it fully, and keep it on a maintainer over the layup.Helpful gear: Battery maintainer — Recommended pick
- Support the cover so snow and rain shed off, and leave vents so the interior can breathe.
- For an inboard or sterndrive, follow the manual closely — those blocks are the ones freeze claims hit hardest.
What to have on hand
As an Amazon Associate we may earn from qualifying purchases. Product picks are editorial; links do not change what you pay.
Marine antifreeze
Propylene-glycol fluid rated for engine blocks and systems.
Recommended pickMarine fuel stabilizer
Additive that protects ethanol-blend fuel over the layup.
Recommended pickFogging oil
Spray that coats cylinders against corrosion in storage.
Recommended pickBattery maintainer
Keeps the cranking battery topped off on the trailer.
Recommended pickBoat freeze damage: the key numbers
Verified national benchmarks; sources open in a new tab (nofollow).
Warm states file the most freeze claims — Texas tops the BoatUS list, ahead of New York and New Jersey, because southern boaters skip winterizing or trust space heaters that fail in outages.
BoatUSCracked engine block repair, often exceeding $10,000 with a replacement long block and labor — versus $100–$800 for professional winterization by engine type.
Discover BoatingTypical boat shrink-wrap cost per foot of boat length; a 21–30 ft boat usually totals $300–$1,000 including arch and tower allowances.
Discover BoatingWhat this means locally
San Antonio freezes later than New Braunfels (Dec 2) and close to San Marcos (Dec 15) — a reminder that even nearby towns differ by days. Statewide, Texas prep dates run Jan 1 through Dec 29, which is why San Antonio gets its own number rather than a Texas-wide average. The same freeze also decides when to winterize an RV and store a motorcycle. Keeping an eye on the rest of the county? The same local math is on our San Angelo page.
Other winter jobs in San Antonio
Every task below is dated to San Antonio's own freeze and snow normals.
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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 15 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 TX 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.
Does boat insurance cover freeze damage?
Usually not by default — ice and freeze damage is excluded from most marine policies as a maintenance issue unless you add a specific rider (roughly $20–$55 per year, typically only purchasable until the end of October). Even with the rider, insurers may ask for proof of proper winterization, so keep the receipt.
Boat Winterization: related searches
Searches this guide answers: winterize outboard vs inboard, boat shrink wrap cost per foot, marine antifreeze ratings, and cracked engine block repair cost.
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Data: NOAA 1991–2020 normals via San Antonio Incarnate Word, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 25, 2026.