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turfguy 07-11-2008 01:02 PM

Marine Diesel Engine Hrs
What would be considered alot of hrs on a smaller marine diesel engine in the 25-50 HP range? In other words would say a 1000 hrs be a level where one could expect alot of work to be needed? Or would 5000 hrs be a time when major work is needed? I do realize how the engine has been maintained is most important, so for this discussion lets assume oil changes were made on time and all other maintence was done. One thing I notice is boats that have been in Charter have lots of hrs for their age, but would assume good maintence too.

Cruisingdad 07-11-2008 01:49 PM

These are my opinions. They are opinions only.

Lots of hours can be a good thing or a bad thing.

I generally like to use the number of about 100 hours/year as average. Less is not always better as that may mean the engine has just been sitting there. A boat which has cruised will have considerably more hours but that is not necessarily bad. Diesels like to be run.

I generally look at around 3000-4000 hours as a rough timeframe when a good overhaul might be required. But a diesel, kept in good condition and maintenanced properely, should run well beyond those numbers. Dad's Tayana 42 has a 42 HP Yanmar with 3600ish hours on it that runs like champ and hardly uses any oil at all.

- CD

bottleinamessage 07-11-2008 03:02 PM

A friend of mine just had his 55HP Yanmar replaced at around 8500 hours.
A well maintained engine should last somewhere in that range, maybe more, as it will somewhat depend on how "hard" the engine was run.

Rockter 07-11-2008 03:19 PM

1,000 hours really isn't much. If it were a road vehicle, running at (say) 60 mph, that would be about 60,000 miles.
Marine diesels will last longer too, as they are not gearchanging and throttling so much.
Change the oil regularly and you will be ok.
Try to keep your revs up, and try to avoid prolonged idling.

speciald 07-11-2008 03:52 PM

Srvice is important. I did major surgery on mine at 2000 hour because it was 2000 hours - new injectors, pickeled heat exchangers, pulled and cleaned turbo and exhaust elbow. Still runs like new and burns no oil. I put a Puradyne oil filter system on 2 years ago and only change oil every 750 hours.

sailboy21 07-11-2008 05:00 PM

Puradyne? Haven't seen a oil filtration system on a pleasure boat but hey, why not? But 750 hrs... that is 5-7 years at what seems to be average use. Last summer I motored about 2000 miles and only put a tad over 400 hrs on the old beast. Even with a purification system I would be worried about keeping oil that long. One thing a filter can not do is replace detergents friction modifiers and other additives needed in modern engines... although I guess replacing oil lost due to normal consumption would replenish some of this. Interesting concept.

turfguy 07-11-2008 05:29 PM

Thanks for all the great comments guys. I really appreciate all your knowledge.

cardiacpaul 07-12-2008 07:31 AM

I just took a look at an '85 Endeavour with a hair over 100 hours, yea, 100 hours on it, and it was the cleanest thing I've seen years.
On the other hand, I know a fella with a perkins 4-108 in a '76 CSY, over 3000 hrs, its as cruddy as a 50 yr old crak who*e, but they both run like a charm.
Oil changes, clean fuel, and first aid before they need it.

Boat engines are like women...

Give them what they want, before they know they want it, and they won't leave you.

chsjohn 07-15-2008 11:39 PM

Don't know if this applies to small engines (don't see why it wouldn't). I know of some diesel engines used in commercial generator applications that have run over 30,000 hours and are still running. These might be a better comparison than an over the road engine that is typicly only running at about 25-40% load. Marine engines and generator drives usually run at much higher loads. Preoilers supply oil under pressure before the engine starter is engaged. The system works by storing oil under pressure and a solenoid valve is opened just prior to starter engagement.. There are interlocks that engage the starter after oil pressure builds up. Start up is probably the hardest thing an engine endures on a regular basis.

Oil temp is also critical for engines running under a high load. Many marine engines have larger oil pans for increased quantity and this will often reduce temperatures to an acceptable level. It isn't uncommon for a marine engine to have a low coolant temp (because of the large quantaties of coolant available), but also havea high oil temp (due to higher bearing loads). Oil coolers are a must for engines running under very high loads, but they also must be properly designed or low oil temperatures will cause damage as well. Thermostatically controlled oil coolers are the best way to go. They function much like a radiator with a thermostat and will modulate the flow of oil or water to maintain proper oil temperature.

It is also criticly important to allow an engines temperature to stabilize after start up (ie: warm up).

Preoilers and oil-coolers don't come cheap, but they can more than pay for themselves in the right application by increasing the engines life.

Just my .02 :)

sailingdog 07-16-2008 02:10 AM


Comparing a commercial generator diesel to a marine diesel isn't really a good comparison IMHO. A commercial genset diesel will run at a fairly constant speed and load, and without the harsh marine environment. Saltwater and humid air does a number on engines... so does the highly variable loading on a boat's engine. Some days you're just idling it to recharge the batteries, others, you pushing it to make the last call at the bar... :)

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