We've got a Perkins 6-354 on 'Tropical Dance'. The Perkins manual says to change the oil every 250 hours. The engine has more than 6,000 hours on her and is running very good given the hours. Compression is slowly getting less but the compression in the cylinders is pretty consistent and in line with an engine of only half her hours. No smoke at all, ever! ( I can't believe I said that)

We change the oil every 100 to 150 hours with 'Delo' or other that's available. I like to use 40 weight (if I can find it) because of the hours on her and the temperature of the water she's in. Since we cruise 6 months out of the year we put somewhere between 3 and 400 hours on her and change the oil about 3 times each year. When we're ready to leave her for a few months I change the oil and run it for about 10 minutes.

Using synthetic oil scares me. I find comfort in changing with new fossil based oil. It's the only way to be certain that there are no contaminants. Changing the oil also gives me a chance to spend some time nosing around the engine. Something that might not take place as much if I used a synthetic.