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Why such a short life span?

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Old 11-24-2007, 03:57 PM
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Can someone explain to me the reasons that marine engines (gasoline) have such a short life span in running hours as compared to vehicle engines, or other equipment with similiar engines?

300 hours, time for top end rebuild, another 300 hours, total rebuild.

Other engines in vehicles, generators, pumps, etc last for thousands of hours without rebuild. What makes these engines so short lived? Is it the fact that the cooling is an open system without radiator?

I was told that the engines are worked very hard while in a boat, at high RPM, not much different than some equipment mentioned above.

Is it the fact that the engine has many high performance mods in it that in itself makes it prone to self destruction at a stock level?

IF that is so, how would a stock vehicle engine last if modded to use the marine cooling system and installed in a boat?

If the same engine was in a vehicle, how would it hold up? Any different?

I have a 454 on a 12" water pump with 3000 hours on it, still running.
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Old 11-24-2007, 04:40 PM
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On diesel engines, "they say" that the time to rebuild is really based on gallons of fuel burned more than on engine hours. That is probably true on gasoline engines too, because fuel burn equals work which probably equals wear.

Say your truck gets 10 miles per gallon. After 150000 miles you have burned 15000 gallons. On a boat that burns 40 gallons per hour per engine, that is 375 hours. Not far off from observation for factory engines run in a fast boat. Boost it up and burn 100 gallons per hour, and 100 to 150 hours and the engine needs a rebuild.

That's probably the key issue.

On my boat, I can only run as fast as the ocean allows, so at 750 hours per engine I've still got good compression numbers, no rod knock, everything seems fine, but I burn about 10-15 gallons per hour per engine, so I should see 1000 to 1500 hours. Seems about right.
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Old 11-24-2007, 05:39 PM
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Marine engines are always under load,its kinda like if you were pulling a house around with your car
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Old 11-24-2007, 06:15 PM
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Quote:
Originally Posted by Mackattack View Post
300 hours, time for top end rebuild, another 300 hours, total rebuild.
Remember those numbers aren't written in stone. It all has to do with operating style and quality of maintenance. You can save tons of rebuild money with an annual (100hr) visual inspection combined with compression and leakdown, and oil sampling at each fluid change. I've got over 1000hrs on my motors. They're past due for major service, but they still run perfect.

Road-going vehicles see no where near the load a boat motor sees. Imagine your tow vehicle pulling your boat around full time, mostly at highway speed, without overdrive. Every so often you mash the pedal to the floor and occassionally you get to coast downhill. How many miles/hours ya' think it would put up with that?
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Old 11-24-2007, 06:23 PM
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I see your point, my 6.0 diesel is already puking coolant while towing my 382.

I guess the difference is the load transfer on the engines.
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Old 11-24-2007, 06:38 PM
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My old stock 454's had over 1,000 hours and still ran OK....500's are a little different. As far as your cars.....put your car in second gear and drive around ALL the time in second gear. Let me know how long your willing to drive on the interstate like that. (but you do it all the time in your boat)
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Old 11-24-2007, 07:14 PM
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has no one developed a multi gear drive? Would this be impossible?, or add too much weight?
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Old 11-24-2007, 07:16 PM
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Gensets run 1800 to 3600 RPM.. Your pump probably is in the 3600 RPM range I would guess..
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Old 11-24-2007, 07:52 PM
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HIgh rpm and high load is the reason. Multi gear transmission would not stop the load cruising or at high speed just get you to speed faster. How often does a car run at 4000-5000rpm at nearly full throttle going up a steep hill? Same thing as a boat on the water.
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Old 11-24-2007, 08:40 PM
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Had the opportunity to ride in a Spectre with Yanmars and ZF two speeds.. VERY odd sensation when it shifted, but man, what a blast!!!
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