I went to look over a boat the other day that had a pair of large
Detroit Diesels (12V-71TIs). The engines are 22 years old, have
about 2,500 hours on them, but appear to have been well maintained.

One thing that concerned me however was that each engine had a block
heater running continuously at 120 degrees (in southern Florida,
albeit winter time). The owner said that he keeps the heaters running
to ensure quick starts.

Can anyone tell me if this is normal practice for these engines, or is
it more likely that the heaters are being used to compensate for
mechanical issues?