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Mercury Ask the Pro

Tuesday, October 10, 2023

Advice on how to clear your engine’s cooling passages in the colder months.

Mercury Ask the Pro answers your questions about boating and Mercury products. For each Mercury Ask the Pro article, we’ll put one of your questions to the Mercury service team, and share their response right here. 

For this installment of Mercury Ask the Pro, we address a question that many boaters have toward the end of the boating season: Is it OK to crank a marine engine out of the water in order to clear the cooling passage?

You may have seen other boaters doing this in the colder months to prevent water from freezing in the engine, and since it’s approaching the time of year when temperatures regularly fall below freezing, you may be concerned that the water in your cooling passages could freeze on your way home from a day of boating or when the boat is stored in an unheated garage.

We asked our Service Product Management team this question, and here is what it had to say.

1. You never want to start your engine outside of the water or without being connected to a water flusher (also known as a water muff). That’s because the impeller requires a constant supply of water when running or it can become damaged quickly.
2. In fact, starting an outboard for the purpose of draining the water is completely unnecessary because outboards are designed to thoroughly drain when trimmed down fully. Simply trim the engine down and give it 5 to 10 minutes for all the water to drain from the engine.  
3. MerCruiser® engines, however, do not self-drain, so a different procedure must be followed to drain the water from these engines. Please consult your owner’s manual or see a Mercury Authorized Dealer.

Remember, the best way to ensure a smooth transition to the spring boating season is to properly winterize your boat the previous fall. You’ll be glad you did!