8v92TA Ocean 48 Sport Fish

Early failure on DD is due to overheating or overloading. If the engines can turn a true (laser/digital tach) 50-100 rpm over their rated rpm with the boat fully loaded then 3-4 thousand hours is not unrealistic. Marine age is the next killer and it sounds like you are already up against that as it sounds like the engines have very low hours for their age. If you are buying the boat then any sea water components over seven years old should be removed, tested and probably replaced. Many of these engines were underpowered or marginally powered for the boats they went into. Everything you asked really depends on the boat. Fuel burn rate is going to depend on the boat and what you consider cruise speed/rpm to be. What boat are they in?

8v92's normally go 1800-2000 hours in a SF, as the other poster said, if you can get them to turn 2400rpms at full throttle, they'll live a happier and longer life then that and some see 3500-4000 hours or more if you cruise them at 1900-1950rpms. The 92 series are less durable and long term then the 71 series. The ones you have will live a lot longer then the 835HP J+T's which would only go 1000 hours probably. They also will live longer being they're in an ocean with a faster cruise. They seem to live a shorter live in the SF's or MY's where they barely keep it on plane 18-20 knots and the load factors (and speed) jump up and down when climbing waves and such.

I burn around a hundred an hour at 1800 rpm with twice the engine (16's)- so a good place to start is 50 an hour at cruise between 1750 and 1900. My winter home is Sailfish Marina on the charter dock. I have less engine issues than nearly every single boat on the dock. Many newer engine the electronics cause issues. I put less hours than most of the guys on the dock but many of the captains openly prefer DD's.

From that description the engines should be fine in that boat. The boat has plenty of power. The cruise speed is well beyond just planing and the spread between WOT and cruise is more than adequate. The engines are on the edge based on rated horsepower but cruising at 34 vs 41 WOT you won't be pulling anywhere near that amount of horsepower out of the engines. Just make sure they turn up full RPM and are properly maintained.

+1. Also an addition of Exhaust Gas Temp gauges on the engines would be a great help and you could keep them cruising with the best fuel/air/load based upon your EGT's....... I think they like 800 degrees if I'm not mistaken.

I put those on my 8V92's (one on each bank) and you are correct, they run almost exactly 800 degrees at cruise speeds +. It is amazing how quickly they drop when you back of the power. If you are down on power and one bank is running cold on the EGT you can go there first to find you problem. They led me right to a stuck injector once.