There's about 2,000 boaters that have made the great loop cruise (6,000 +
miles) without selling their boats at the end. Gasoline engines with fresh
water cooling and good heat exchangers run very cool - proper maintenance is
required to keep through-hulls and cooling lines clean, but actually the
long runs are better on the engines than short weekend jaunts to a nearby
cove. Raw water cooling requires more maintenance, but in the fresh water
rivers cooling systems will be o.k.
The salt water will kill off any algae in the cooling system at the end, but
a haul out in Miami and a good cooling system cleanout is advisable with raw
water cooling.