will my boat engine freeze

Will My Boat Engine Freeze – Everything I have Learned

With all of the freezing temperatures that we have had lately, It’s hard not to wonder about my engine and if I should be concerned about it freezing or not.

After doing many hours of research on the topic, I was able to put together a helpful informational guide that I would like to share with you.

Engines that are not properly winterized run the risk of severe damage, such as cracking, which is caused due to water freezing inside of the engine from cold temperatures — rendering even the best engine useless.

Will An Outboard Motor Freeze

An outboard motor that is not correctly drained before storing it for the winter will freeze. I read that it is suggested for you to store your engine in the down position. Another thing I learned that some people do before storing the motor is that they turn the kill switch to off and then turn the engine over using the key. This will help blow out any extra water left inside.

Of course, if you properly winterize your outboard before putting it away for the winter, you should be fine.

Do You Need To Winterize A Boat

If you live in a location where the temperature gets near or below freezing during the winter months, then you will want to make sure that you properly winterize your boat.

Something I was surprised in reading was, even if you live in certain parts of California, you should still be winterizing your engine. Many places in California get frost and temperatures below 32 degrees Fahrenheit.

For more information on winterizing your boat, take a look at my article titled “Everything You Need to Know For Winterizing a Boat.”

Do You Need To Winterize a Boat That Is Stored In a Garage All Winter

If you live in a location that gets below freezing temperatures, especially for multiple days straight, then you should still winterize your boat even if it is stored in a garage all winter.

Even though your boat is in a garage, if the temperature outside drops below freezing, a bucket of water could still freeze in that temperature unless your garage is heated.

But even if your garage is heated, what happens if you have a power failure and your heat is off for 24 hours? Or you, your wife, or one of your kids leave the garage door open all day? By not winterizing the engine, that could be a risky gamble that you don’t want to try taking.

What Temperature Will Water Freeze In Engine

Different factors would have to come in to play that would need to be considered to know when the water in your engine might begin to freeze or not.

  • If you have an engine that is raw water cooled in freshwater from like a lake or a river and water is left in your lines, then the temperature would have to fall below 32 degrees Fahrenheit for several hours. When that happens, the water inside will begin to freeze which will lead to cracking the block.
  • Saltwater cooled engines with some saltwater left inside don’t freeze as quickly or at the same temperatures as freshwater. Saltwater freezes typically at temperatures below 27 degrees Fahrenheit.
  • A freshwater, anti-freeze cooled engine would only have some raw water in the oil cooler and the heat exchanger.
  • A boat left in the water overnight should be okay. The surrounding water will keep it from freezing.

To determine at which temperature water would freeze in the engine depends on what the water to anti-freeze ratio is that it is in the engine.

For example, you could use a 100 percent ratio of a marine anti-freeze that will protect your engine from freezing in temperatures as cold as -50 degrees Fahrenheit. Some brands will even protect your engine up to -100 degree Fahrenheit.

Now that is only if you can get 100 percent of the water out of the engine block and lines. If any water is left inside, that would mix with the anti-freeze and dilute it so that it will freeze sooner.

Another example is if you have 50 percent water and 50 percent anti-freeze in the engine, the temperature at which the combination of the two might start to freeze between -20 to -35 degrees Fahrenheit, even though the anti-freeze is rated for -50 degree Fahrenheit temperatures.

There is an inexpensive tool that you could buy on Amazon called a hydrometer that will accurately tell you what your freezing point is for what you have in your engine. The tool has hundreds of good reviews for a reason. Click here for the current price on Amazon.

If you are not using any anti-freeze, and you only have water in the engine and lines, then the water will begin to freeze at 32 degrees Fahrenheit and below.

One other thing you need to keep in mind is the amount of time that the engine is sitting in freezing temperatures. If it is left for a few hours, then that would probably not affect it very much. However, if it were left overnight in those temperatures, then it would have a greater chance of freezing.

boat engine freeze

How to Keep Boat Engine From Freezing

If you know the temperature is going to be below 32 degrees Fahrenheit overnight, one thing you could do late in the evening is run the engine to temperature, then close the engine cover. Doing this should help keep the engine warm enough to last several hours.

Another thing that is suggested is that you use an anti-freeze that is specific for Marine use only. Marine anti-freeze is a propylene glycol-based product, where the stuff used in cars is an alcohol or ethyl alcohol-based product.

Ethyl alcohol-based products are corrosive, especially to rubbers, which will eat away at your rubber hoses, seals and gaskets.

Propylene glycol will lubricate and coat the inside of your engine and hoses to prevent them from any corrosion over the winter. Marine anti-freeze is good for up to -50 degrees Fahrenheit.

If you choose not to use an anti-freeze, you must make sure that you have fully drained any remaining water that’s been left inside the engine and lines. When water freezes, it will begin to expand which is what causes the engine to crack and lines to burst.

How to Keep Boat Engine Warm in Winter

One method to help keep your inboard boat engine warn during the winter months is by using a bilge heater. A popular choice is the Xtreme Heater XHEAT 300W 110V Bilge Engine Compartment Heater. This will help you get away from having to winterize your boat and opens up more opportunities for you to be able to enjoy those beautiful days during the winter and allow you to get more use out of your boat without having to perform the winterization each time.

Xtreme Heater

What the Xtreme Heater does is that it creates a pocket of warm air that is stored within your engine compartment, keeping your engine and hoses from freezing. These heaters are ABYC certified and deemed to be one of the safest options to keep your engine compartment warm.

I read a valuable point on a message board from one user who stated that you should never use an electric blanket, bulb, socket, or switch to try keeping your engine warm in the water. The reason for this is because the fumes from the gasoline could collect in the engine compartment. A slight spark caused by an electrical device could cause an explosion.

Before you purchase an Xtreme Heater XHEAT, it is recommended that you speak to your local marine dealership, or boat manufacturer to determine what size of the heater you would require for your sized compartment.


Although it might seem like a pain to winterize your engines, and it might cost you a little extra money, it’s still the best way to help protect your engine during the winter. Come the spring; you’ll be happy that you did.


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