Marine Diesels vs Truck Diesels

[kd3pc]

elgo...

you may want to start your own thread on this...

but here you go...Yanmar 55 hp....I would suspect a 4jh2 series and with proper maintenance and repair, clean fuel and air...you should be able to get 5-7,000 hours on it. They are very solid engines.

They do need to be run at speed, load, and regularly.

What color exhaust can lead you to some conclusions, but testing of the crankcase oil is a better way to see for sure. If the PO did analysis, you can tell, else you will need to start your own history.

All the best and welcome

[smurphny]

Marine engines specifically designed for this type use are engineered for constant torque, unlike auto/truck engines which are designed to have lots of "coast" time and to run at widely varying rpms. Industrial engines have the same design factors. That's why a small block V8 works great in boats but usually for few hours. It was never really meant to take the constant torque of a propeller pushing a sailboat for days at a time at the same rpm. Truck gassers like the 440 were a bit better, with a longer stroke but none of the auto conversions will perform for that many hours at constant rpms. That's why work boats use Cat or GM diesels to drag trawl nets day after day. Size has little to do with it, it's the bore/stroke, and materials used that make a marine diesel different.

As far as low rpm "babying" a Yanmar or any small diesel...it's a good way to start it smoking and to wind up practicing your ring job skills. They like to be (have to be) mostly run at around 2800 rpm, at the top of their torque curve.

[steel]

Here's what happens under no load:

There's low combustion temperature, which causes incomplete combustion of the diesel and then acids will form. The oil will need to be changed frequently because of this.

Low engine temperature. This just causes extra wear.

Glazing of cylinders.

Carbon buildup. The engine needs to be run under load for a while to clean this up.



The newer diesel truck engines use very high injection pressures which causes the diesel fuel to burn much better even at no load so modern truck diesels aren't harmed as badly. Older truck engines were harmed just as badly as marine engines.

It would be better to have the engine run at higher load than to have it run at higher RPMs because the latter puts more wear on the engine and wastes more fuel. With the higher RPMs method all you're doing is creating more friction in the engine so that you can put more fuel in the engine to keep the temperature up a bit. At higher RPMs you're running more air through the engine which cools it off even more so it is not nearly as good as putting the engine under some load.

How about having the engine run at idle or a little above idle and then put a full load on the alternator with some device like a 12 volt heater or 12v water heater element that you put through the hull? Or get an over sized alternator just for the purpose of putting load on the engine when it is idling.

And one more thing: You can disable some cylinders on the engine so that the other cylinders can run with say twice as much fuel and have the proper combustion temperature. That doesn't help the low engine temperature though.

[mitiempo]

An oversize alternator won't put that much load on a sizable engine. On a 10 hp engine it would. But an oversize alt, if not needed, is also expensive.

An alternator will use about 1 hp per 25 amps of output. Above 100 amp output a single belt has to give way to a serpentine belt which also adds to the cost.

[rpeebles]

Is that a good way to heat up engine if it is not possible to leave the dock? Or does that put too much stress on engine?

[mitiempo]

Not on the engine, just on the dock.