"Working an engine "fairly
"Working an engine "fairly hard" is sometimes misleading on it's face. The engine wants to be up to temperature and be working at an efficient level. So, if you run at 1400 RPM and the temp is at 170 then the cylinder is not as hot as it's designed temp, possibly allowing carbon to build up slowly over time in the ring lands and top or pistons, valves, etc.
The moisture in the oil doesn't get evaporated as quickly. Especially if you typically run short runs which I would put at under an hour. (purely arbitrary number)Do you know someone who runs their boat in the slip for 15 minutes every couple of weeks in the winter? (typical in my area PNW where we are in the water year around) If they don't load the engine by running in gear they aren't building up the heat to clean everything up.
Many engine manufacturers used to recommend running wide open for 15 minutes or so every X number of hours of running. This was to make sure everything was cleaned up. Running at WOT every so often will also alert you to developing cooling problems.
Lehman 120's like clean oil, they like the injector oil changed often (I do mine every 50 hours, the book recommends at least every 100 hours). They like clean fuel even though their tolerances are not as close as modern engines.
Warm up your engine properly. Don't let it idle for too long after a cold start. Start the engine, unplug, untie and idle out. Don't leave the marina, get outside the breakwater and run up to cruising RPM. Instead run it up to 1000 RPM or so and let the heat build up to 160/170, then bump it up to cruising R's. This takes about 10-15 minutes in my boat.
Imagine taking a glass out of the freezer and putting the hottest part of the tip of a propane torch to the side of it immediately. What would you expect to happen to the glass? Or, take the glass out of the freezer and slowly play the feather edge of the flame over the glass, watching the ice crystals melt and run off, then getting a little closer and playing the flame, watching the glass get hotter. Finally you can take the flame and put the tips hottest portion directly on the glass until it melts. Which way would work best for your engine?
The same is true when shutting down. Let it cool while approaching the marina, idle in, let the temp go back down to 160 or so before shutting off. This is a little easier to do since it generally takes about the right time to get in and tied.
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