Dear Boat Doctor,
I own a Hunter 33 that I keep on Lake Michigan. My marina is really easy to get in and out of so I really don't burn a lot of fuel. I usually go through less than a tank of fuel per season. Every fall I add an algaecide to my fuel, but since I have pre-treated fuel at the end of the season, should I add the prescribed amount or something less?

Dear Ben,
Your relatively simple question has a multifaceted answer. First off, within reason, I would add a bit less fuel treatment to your fuel tank. My larger concern is that you are not running your engine long and hard enough. A diesel engine needs to be run for a while at cruising temperature to be happy.

A good rule of thumb is to run a diesel engine at temperature for about an hour once every month or so. When an engine is first started, a bit of fuel is lost into the oil, and as the engine runs moisture and contaminants are absorbed into the oil. As the engine is run at a warm temperature, the oil heats and releases the moisture, fuel and contaminants. Failing to do this keeps the contaminants in the oil and has the potential to damage internal engine components.

The cold lake water that you run in does a really good job of keeping the engine cool and thus you may need to run a little longer than an hour to make sure the engine comes up to temperature.