Stella Blue  was first commissioned using Shell Rotella T 15W 40 diesel engine oil. I have always held that Shell was an industry leader in petroleum products, so I continue to use it in the boat. I buy the oil at Sam's Club for about $37.00 for a 6 gallon case (2005 pricing), which is way less than the boat yards get for a 5 gallon can. The book says the Yanmar 370 will hold 20 quarts of oil including the oil filter. The first time I changed the oil, I found that 16 quarts was more than enough to bring the level up to the full mark on the long dipstick, found near the top of the engine on the port side. What I didn't know is, there is a short dipstick that is more accurate , on the lower starboard side of the engine. The long dipstick was added as a convenience, but some were not marked correctly, which may be part of the problem showing full at 16 quarts of oil. I also think there is much oil that remains in the oil lines and  cooler that do not completely drain, that contributes to the "16 quarts full" problem. Unless you've been told about this second dipstick, you would probably never look for it after seeing the long one. It is located just ahead of the oil cooler and the hole is right in the oil pan. Here is a picture to help find it.

dipstick

Norm Blinn from the Yahoo E-group "Mainship" pointed this out to me, and suggested this dipstick should be used to determine the correct oil level in this engine.

Thanks Norm, for the pointer.