I grew up with Detroits. When I came around they were still Gray Marine
. The 671 was the most common. As a kid I worked on the river and most engines were Detroits. Many were WWII built engines. What I like about them is that they are mechanical. No electrical parts
except for the starter. The injectors are fired by the cam. Once it's started it will run as long as fuel
is available. No circuit boards, no wireing, no expensive computer box. They are rebuildable many times. Most of the accessories and injectors are rebuildable. Parts
are available everywhere. Many aftermarket part manufactures keep prices reasonable.
I have 671 mains about to be rebuilt. They have much more than 10,000 hours. Who knows when, if ever they were rebuilt. The blocks are about 60 years old. Other than some smoke, especially at start up, they still run fine.
My boat was built as a patrol boat with a semi planing hull
. 83', about 80 tons. The 671s push this boat at 10 knots using 10 gallons an hour at 1800rpm. When I bought the boat it used 14 gal/hr. @ 10 knots. With a little work you can gain some economy if you're not in the upper 20% of horsepower. Detroits run at high rpm
don't last as long, but neither do most other engines. There are other fine engines. Many get better economy. But I don't feel any of the engines with electronic controls are reliable. They'd be ok in trucks, but not out to sea.