I had my 1981 2GM completely disassembled and rebuilt 2 years ago. Due to my own stupid mistake, one of the pistons seized. The piston and cylinder sleeve had to be replaced. But, I was able to inspect the engine as it was disassembled. The parts all looked brand new! Except for a little scale in the cooling water passages, everything looked quite good. Not surprising when you consider the typical engine usage - motoring a few minutes in and out of the slip a few times a month. Add that up over 20 yrs, I think you'll find that the actual engine usage is probably less than your car's engine with 10,000 miles. Figure you motor 5 minutes in 5 minutes out of the slip, once a week for 20 yrs, thats 173 hrs. If you drive your car at 60mph for 173 hrs thats a little more than 10K miles. Do you worry much about your car's engine when it has 10k miles? So, how much longer can a 20 yr old Yanmar run? I guess it depends on how it has been used and maintained. My old Jeep has 156,000 miles and it still runs like a champ, my 20 yr old Yanmar runs great too.
