Generator Won’t Start in Cold Weather? 7 Causes and Fixes

Updated: February 1, 2026

When temperatures drop and you need your generator most, the last thing you want is a machine that won’t start. Cold weather creates unique challenges for both portable and standby generators.

This guide covers the 7 most common causes and how to fix them.

Why Your Generator Won’t Start in Cold Weather

Cold temperatures affect generators in several ways. Batteries lose a significant amount of their cranking power as temperatures drop. At 0°F, a battery only has about 50% of the power it would have at 80°F. Oil also thickens in the cold, which makes the engine much harder to turn over.

Fuel systems can freeze too, especially propane regulators and fuel lines that have moisture in them. Even metal components contract in the cold, which can cause tight tolerances and stuck parts.

7 Common Causes and Fixes

1. Weak or Dead Battery

This is the number one cause of cold weather starting problems. Cold temperatures dramatically reduce battery capacity, so a battery that works fine in summer may not have enough power to crank the engine when it’s freezing.

You’ll usually notice slow cranking or a clicking sound when you try to start. The starter might turn slowly and then stop, or you might see the dashboard lights dim when cranking.

To fix this, test your battery voltage first. It should read 12.6V or higher. If it’s low, charge the battery or use a jump pack to get it started. Batteries older than 3 years often need replacement, especially if they’ve been through a few winters. Keeping your battery on a maintainer during the cold months helps prevent this problem.

2. Oil Too Thick

Standard 10W-30 oil thickens significantly in cold weather, making the engine much harder to turn over. If you’re using a pull-start generator, you’ll notice the cord is very hard to pull. With electric start, the engine will crank very slowly and sound labored.

The fix here is simple: switch to synthetic 5W-30 oil for cold weather operation. Check your owner’s manual for specific cold weather oil recommendations. In extreme cold (below 0°F), some generators may need 0W-30 oil to start reliably.

3. Choke Not Engaging Properly

Cold engines need a rich fuel mixture to start. If the choke isn’t closing fully, the engine won’t get enough fuel to fire up. You’ll notice the engine cranks but won’t actually start, or it might start briefly and then die. Some generators will only run if you manually hold the choke closed.

First, make sure the choke is set to the CLOSED or START position. Then check that the choke plate moves freely without sticking. If there’s debris or varnish buildup on the choke mechanism, clean it off. For generators with automatic chokes, the thermostat element might need inspection or replacement.

4. Stale or Contaminated Fuel

Gas degrades over time, and old fuel causes starting problems that become even worse in cold weather. If your generator cranks but won’t start, or starts rough and runs poorly, stale fuel might be the culprit. Give your fuel a sniff. If it smells sour or like varnish, it’s time for fresh gas.

Drain the old fuel completely and replace it with fresh gasoline. Going forward, use fuel stabilizer in any gas you plan to store. Ethanol-blended fuel should be used within 30 days if you’re not using stabilizer. For longer storage, consider ethanol-free fuel which has a much better shelf life.

5. Frozen Fuel System (Propane/Natural Gas)

Propane and natural gas generators are especially prone to cold weather issues. Moisture in the regulator can freeze and block fuel flow, and propane doesn’t vaporize well in extreme cold. The typical symptom is an engine that cranks fine but doesn’t seem to be getting any fuel. It might run briefly and then die, or work fine when it’s warmer but fail when temperatures drop.

Check your regulator for any visible ice or frost. If you find some, warm it gently with your hands or a warm cloth, but never use an open flame. For long-term solutions, consider installing a regulator heater or cold weather kit. Using larger propane tanks also helps because small tanks can’t supply enough vapor pressure in the cold. Make sure your regulator’s drain hole is facing down so moisture can escape.

6. Carburetor Issues

Carburetors can develop ice inside when cold, humid air passes through them. Varnish from old fuel also causes sticking that gets worse in cold weather. You’ll typically see the engine start and then die after a few seconds, or experience a surging, hunting idle. The generator might only run properly with the choke engaged.

Let the engine warm up slowly with the choke on before trying to run it normally. Carburetor cleaner spray can help dissolve varnish and ice. Check the fuel bowl for water, which can freeze and cause blockages. For generators used regularly in extreme cold, a carburetor heater is worth considering.

7. Spark Plug Problems

Cold weather can expose a weak spark that would work fine in warmer conditions. If you’re getting no spark or weak spark, the engine will crank but never actually fire. Starting might be intermittent, working sometimes but not others.

Remove the spark plug and inspect it. Check the gap against your generator’s specifications and adjust if needed. If the electrode is worn or damaged, replace the plug. Also make sure the plug wire connection is tight and free of corrosion.

Need help choosing the right spark plug? See our spark plug comparison guide.

Cold Weather Starting Tips

A few simple preparations can make cold weather starting much more reliable. Using synthetic oil makes a big difference because it flows better in the cold and makes cranking easier. Keeping your battery fully charged ensures you have maximum cranking power when you need it. Even storing your generator in a garage or shed helps. Being just 10°F warmer than outside can make starting significantly easier.

Running your generator monthly prevents fuel from going stale and keeps all the moving parts lubricated. For standby generators in cold climates, installing a cold weather kit with block heaters and battery warmers is worth the investment.

Generac Cold Weather Kits

If you have a Generac standby generator, they offer cold weather kits designed for extreme climates. The standard Cold Weather Kit (part numbers 7101, 7102, 7103 depending on your model) includes a battery warmer and oil heater. For temperatures below -20°F, the Extreme Cold Weather Kit adds a block heater to keep the engine itself warm.

These kits keep critical components at a temperature where they’ll function properly, so your generator starts reliably even in the coldest conditions.

When to Call a Professional

Some cold weather issues go beyond what you can fix yourself. If your battery keeps failing even after replacement, there might be a problem with the charging system. Gas pressure issues on natural gas generators require a technician to diagnose safely. Internal engine problems and error codes that won’t clear also need professional attention.

For Generac standby generators, call 1-888-GENERAC or contact your local authorized dealer.

Frequently Asked Questions

What temperature is too cold for a generator?

Most generators can start down to about 0°F (-18°C) with proper preparation. Below that, you may need cold weather kits, block heaters, or indoor storage. Check your owner’s manual for specific temperature ratings.

Should I let my generator warm up before putting a load on it?

Yes. Let it run for 2-3 minutes before connecting loads. This allows oil to circulate and the engine to reach operating temperature. Adding full load to a cold engine causes extra wear.

Why does my propane generator work in summer but not winter?

Propane doesn’t vaporize well in extreme cold, especially from small tanks. The regulator diaphragm also stiffens in low temperatures. Use larger tanks (100lb vs 20lb), install a regulator heater, or store tanks in a warmer location.

Can I use starting fluid on my generator?

Use it sparingly and only as a last resort. Starting fluid can damage seals and wash oil from cylinder walls. A few short bursts while cranking is usually safe, but regular use indicates an underlying problem that needs fixing.

How do I keep my generator battery charged in winter?

Use a battery maintainer (trickle charger) connected whenever the generator isn’t running. For standby generators, the built-in charger should keep it maintained. Check battery voltage monthly and make sure it stays above 12.4V.

My generator ran fine yesterday but won’t start today. What happened?

Temperature likely dropped overnight. The battery may have lost enough capacity that it can’t crank the cold engine. Try charging or jumping the battery, and switch to synthetic oil for easier cold starts.

Conclusion

Cold weather generator problems are frustrating, especially during a power outage when you need it most. The good news is that most issues come down to a few common causes: weak batteries, thick oil, and fuel system problems.

Prepare before winter hits by switching to synthetic oil, keeping batteries charged, and running your generator monthly. For standby units in extreme climates, consider installing a cold weather kit.

With proper preparation, your generator will start reliably even when temperatures drop below freezing.