FrostList

When to Winterize Your Boat in Fort Collins, CO

ON TRACK98 days until first 28°F freezeOct 17

Plan to haul out and winterize your boat in Fort Collins by October 10. The first 28°F freeze near Fort Collins averages October 17 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 15 days before the median.

OUTLOOK

Typical first first 28°F freeze near Oct 17; local deadline about Oct 10. The live 10-day outlook loads here.

Local freeze dates for Fort Collins

ThresholdEarly (1-in-10)MedianLate (9-in-10)
32°F (light freeze)Sep 24Oct 7Oct 20
28°F (hard freeze)Oct 2Oct 17Oct 28
24°F (severe)Oct 12Oct 26Nov 8

NOAA station: Ft Collins · 0.6 mi away · 5,004 ft elevation.

Numbers for Fort Collins come from Ft Collins, 0.6 miles away at 5,004 feet, where the medians fall 32°F by Oct 7, 28°F by Oct 17, 24°F by Oct 26. The 28°F freeze has come as early as Oct 2 and as late as Oct 28, a 26-day spread. Spring's last 32°F freeze clears around May 2. Snowfall averages 51 inches a year, first reaching an inch near October.

Expect the first frost near Oct 7 in Fort Collins and the first hard freeze by about Oct 17. That first freezing night has ranged from Sep 24 to Oct 20, roughly a 26-day spread. On the spring side, the last 32°F freeze clears around May 2 and as late as May 14 — the green light for reopening water and de-winterizing. Snow totals near 51 inches a year mean plowing and ice-dam control share the winter to-do list here.

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

Fort Collins freezes later than Loveland (Oct 10) and close to Greeley (Oct 18) — a reminder that even nearby towns differ by days. Statewide, Colorado prep dates run Oct 3 through Oct 26, which is why Fort Collins gets its own number rather than a Colorado-wide average. The same freeze also decides when to winterize an RV and store a motorcycle.

Other winter jobs in Fort Collins

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

Sprinklers → Oct 7Frozen pipes → Sep 24Ice dams → Sep 15Car battery → Oct 17Snow blower → Sep 24Sump pump → May 2RV → Oct 7Motorcycle → Oct 7

See the full Fort Collins 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 Oct 17 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 CO 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 Ft Collins, live outlook by Open-Meteo. Sources · Methodology. Last updated: July 11, 2026.