Marine Gas Engine Life Expectancy

I would say 1500 hours is a reasonable number for gas inboards. BUT, I've seen many many of them die under 500hours because a lot of gas inboard owners are cheap and don't do the proper maintanence and don't change exhaust manifolds and risers every 5 years or overheat them. I've also personally known gas inboards that have gone 4,000 hours with no rebuilds. But you see many die an early death. A compression test, seatrial, check exhaust manifold riser temps at cruise speed and good oil pressure would be your best guide to their current condition rather than hours. Also keep in mind, that there are a lot of VERY heavy boats that should never have gas engines in them, with gas inboards like all of those 40'+ carvers, silvertons, sea rays and others they threw them in.

I have used 2 surveyors on the Eastern Shore for my own personal yacht purchases. Both will do and have done gas engine compression tests. Reno Panico, Atlantic Seaboard Marine Surveyors and Steve Sanders, East Coast Surveying. Both are SAMS surveyors and their contact may be found on the SAMS site along with plenty of others. Membership Roster for Maryland

Got it. I replied. Call my cell if you want to talk.

I agree with Capt J but in many cases even not so heavy boats have the wrong size engine to power them. I currently have a Carver 3607 that weighs around the 20,000lb mark and she is powered with twin 8.2L Blue Water Mercruisers, which I think is adequate but at the limit. The boat would be better off with diesels, but it all has to do with the cost.

There are boats in my marina about the same size with 5.7L Mercs and they average about 1500 hours before re-builds.

I see many 20 - 30 foot boats that are way under powered and it seems to be related to cost. My neighbour had a 25 foot Searay with a 5.0L Merc and it needed a re-build at 550 hours.

To me, the manufacturers and marinas should consider the life of an engine when coupling it with a hull rather than the current attitude to make it as financially attractive to a buyer.

This topic is a sore spot to me because I have seen too many young people that try to get into boating and after just a couple of years need to rebuild the engine because it is not the right one for their boat.

Lifespan greatly varies between FWC and RWC engines. FreshWaterCooled motor can last 1500 hours with minor maintenance, while 500 hrs on the RawWaterCooled motor is about the limit, even with regular flushing after use. On diesel engines it is quantity of fuel passed through the motor that determines lifespan.

This was always something I saw on lakes. We had just a 30' bowrider but had the largest engine options (430 hp) versus many who were buying with the smallest (300 hp). In Mercruiser you're talking the 8.2 Mag vs. the 350. Volvo the model is 430 CE vs. 300 C. We didn't have it really because of the top end speed but because we felt we taxed it a lot less in normal operation. Where those with smaller engines are running WOT we'd be running a comfortable 2/3 cruising speed. We did have regular service, used the boat constantly, and never shut it down for winter or winterized it. Rarely did it ever go more than a week between uses and never more than two weeks. Never out of the water except for service and bottom cleaning. When we sold it, it had 1200 engine hours and ran perfectly. Reached the same RPM's and top end as the day it was new.

I saw the most disappointed boat users were those with underpowered boats and they were also the ones with the most problems. Now this doesn't carry over to larger boats, displacement and semi-displacement, and diesel installations. I'm just talking about gas engines in modest sized boats intended as planing boats. The reason for the underpowering is simple. Cost. And the dealer isn't about to tell you in most cases that you'll be unhappy with it.