Review: Yanmar 3YM30AE marine diesel

By: Andrew Norton

With the 3YM30AE, Yanmar has done a great job of improving on a great marine diesel engine.

Review: Yanmar 3YM30AE marine diesel
Boats powered by marine diesel engines like the Yanmar 3YM30AE saildrive are likely to command a higher resale value compared to other marine engines.

Not that long ago I reviewed the recently released Yanmar 3YM30AE, designed to replace the long-running and incredibly popular Yanmar 3YM30 marine engine. I tested twins mounted in a Lagoon 38 cat a while back now and was way impressed with their smoke-free running, great midrange torque and excellent fuel efficiency, especially combined with the brilliant Gori overdrive folding props.

Yanmar has done a supersize trick by increasing the piston displacement to enable the engine to develop the same power but at lower rpm, and slightly boost torque output to 76 Newton metres at 2000rpm compared to 69.5 at 2000 to 2500rpm. Yet the overall shaftdrive package is only 4kg or three per cent heavier. And even better, the new engine has the same footprint as the 3YM30 so repowering is a cinch.


Yanmar 3YM30AE

The new marine diesel engine is not just a "stroked" or bored-out version of the older unit but has completely new cylinder bore and piston stroke dimensions. The bore is the same as the long-gone Yanmar 3HM35 which developed 33.5 brake horsepower at 3400rpm from 1282cc but the stroke is slightly shorter.

Like all mechanically-injected marine diesels engines the Yanmar 3YM30AE shouldn’t be run for extended periods at low rpm or the cylinder bores may glaze due to excessive fuel supply below the fixed injection timing. Far better to operate between 1800 and 2800rpm to maintain a reasonable engine load. The Yanmar 3YM30AE has the torque in twin-engine installations for power sailing cats to 12m or as single-keel boats to 10m.

This marine diesel engine was available with raw (sea) water cooling or heat exchanger, but from the Yanmar 3YM30 onwards the engines have been heat exchanger cooled. Running at hotter temperatures with a more constant range reduces exhaust emission levels and eliminates the possibility of seawater entering the combustion chambers should the cylinder head gasket fail.

Obviously there’s more maintenance as the freshwater circulating pump needs checking as well as the rubber seawater pump impeller, but as the 3YM30AE has an industrial base engine it’s running as it was designed to, always a good thing with an engine!

As with the Yanmar 3YM30 marine diesel, the new engine has a gear-driven camshaft and pushrods to operate the two valves per cylinder. Simple and reliable; thank heavens Yanmar hasn’t cheapened-out and used a belt-driven overhead camshaft.

At 125amp the voltage-regulated alternator has an impressive output relative to engine output and is mounted high up on the engine just below the heat exchanger crown. Even the 1.4kW starter motor is mounted well above the engine bearers. Sensibly there’s no shroud covering the V-belt that runs the freshwater pump and the alternator as Yanmar logically assumes no-one would be daft enough to go near this part of the engine when it’s running.

A sump evacuation pump makes changing oil easier and though Yanmar doesn’t stipulate the oil viscosity, I recommend SAE 10W30 for cooler climates or SAE 15W40 for the tropics. Just make sure you use a specific mineral-based diesel engine oil.

The 3YM30 measured 716mm long, 462mm wide and 618mm high with the mechanical straight-output gearbox, whereas the 3YM30AE is 715 x 485 x 619mm including the same KM2P-1 box. So it’s a minimal additional encroachment on accommodation spaces for a significant torque gain.

The KM2P-1 box is available with ratios of 2.21:1 or 2.62:1 ahead and 3.06:1 astern. I’ve always liked Yanmar’s idea of having a deeper astern ratio as the engine can reach its torque band faster when coming alongside a jetty. For cruising yachts I’d opt for the deeper ratio ahead and for racing yachts the taller ratio. Being mechanical both boxes can handle a freewheeling prop under sail where there’s insufficient space to fit a folding prop and both weigh 10kg.


Yanmar saildrive

Yanmar’s new SD25 saildrive is the other option and weighs 30kg. However it still retains the dog clutch of the long-running SD20 drive leg and the same 2.64:1 gear ratios ahead and astern. So no rapid shifting with this box, but of course it can be fitted with the brilliant Gori overdrive prop which increases prop pitch by around 17 per cent when in this setting. It’s like having a variable pitch prop without the complication of a hollow prop shaft for the pitch control rod. The SD25 has an easily-reached oil filler cap and the cooling water intakes are at the aft end of the leg where they’re less likely to be blocked by weed.

The standard instrument panel includes an analogue tachometer (though rated to 5000rpm, how annoying!) and a digital LCD engine running-hours display. Flanking the tacho are stop/start switches, including glow plugs for the indirect injection system and a separate key switch. Very neat and compact.


The Trade-a-Boat verdict

Ever since Yanmar’s big push into the local market in the early seventies the company’s marine diesel engines have been sought-after units. Apart from some niggling issues with the early units the current models are well-engineered, though parts pricing can vary widely depending on the supplier. But it’s comforting to know that your boat will probably fetch a higher resale value powered by diesel Yanmar engine than most other makes.

More information: visit


Yanmar 3YM30AE performance

Single 28.6hp Yanmar 3YM30AE marine diesel engine.













































* Sea-trial data supplied by the author.


Yanmar 3YM30AE specs

TYPE Three-cylinder indirect injection four-stroke marine diesel engine

RATED BHP/MHP* 28.6/29.0 at 3200rpm

MAX TORQUE 76Nm at 2000rpm


BORE X STROKE 80 x 84mm

WEIGHT 137kg (dry, w/gearbox); 157kd (dry, w/ saildrive)

* Brake horsepower/metric horsepower or PS


See the full version of this review in Trade-A-Boat #261, on sale December 28, 2015. Why not subscribe today?

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