Review: Yanmar 3JH5E

By: Andrew Norton

The Yanmar 3JH5E is an under-stressed boat engine that should last a lifetime if properly cared for.

Review: Yanmar 3JH5E
The Yanmar 3JH5E marine engine should last a lifetime if properly cared for.

In a crowded market where most diesels of its output are of tractor-origin, four-cylinder and indirect injection, the 3JH5E from Yanmar Diesel engines is the odd on out. But that ain’t necessarily a bad thing. The Yanmar 3JH5E boat engine has tons of torque at relatively low rpm and better fuel efficiency than the indirect competition relative to torque output.

Unlike indirect injection, where fuel is sprayed into a small pre-combustion chamber before mixing with air in the cylinder, direct injection sprays fuel directly atop the piston, giving more power and torque from each litre of fuel used.

Traditionally, direct injection diesels had higher exhaust emissions than comparable indirect units, so most naturally aspirated engines were indirect to burn the air/fuel mix more thoroughly.

Improvements in injector design and higher fuel spray pressures have reduced the gap through to where a naturally aspirated direct injection engine can meet current emission levels, as is the case with the Yanmar 3JH5E. However its three big cylinders will create higher vibration levels than the four-cylinder competition, so if you’re repowering a timber hull make sure the engine has flexible mountings and prop shaft couplings.



With its slightly under square cylinder bore/piston stroke dimensions and gear driven pushrod operated valves, the Yanmar 3JH5E was obviously designed for a long service life. Standard is heat exchanger cooling with no option for keel cooling, allowing for flexible exhaust gas piping out to the transom.

Yanmar has fitted a shroud to prevent stray fingers from accidentally damaging the alternator and freshwater cooling circulating pump v-belt. The seawater pump with rubber impeller is gear-driven from the camshaft. A 12V 80amp voltage regulated alternator is fitted with provision for mounting a second unit of 80 or 130amp or even a 24V 75amp unit, though slightly lower to starboard than the standard high-mounted unit to port.

The sump oil filter is mounted on its side to starboard of the engine, reducing spillage when replaced. Sensibly the sump oil evacuation pump draws from the aft end of the sump so that when the engine is inclined, most of the old oil can be removed – nothing more frustrating (for nerds like me) than not being able to remove all the old oil when changing it.

Yanmar doesn’t state the sump oil SAE requirement but I suggest either SAE 30 monograde or SAE 15W40 oils rated for marine or truck diesel engines, not petrol and diesel car engines as marine engine duty cycles are totally different. The oil and filter should be changed every 200 hours or annually, or every six months if using the engine infrequently.

For its output the Yanmar 3JH5E marine engine is fairly bulky and with the KM35A mechanical cone clutch and seven-degree down-angle output gearbox it’s 770mm long, 517.6mm wide and 622.6mm high. As with its less powerful counterparts this box has a choice of ahead gear ratios and one astern ratio.

For yachts the 2.33:1 ahead and 3.04:1 astern option means the engine can quickly meet its torque band going astern without overloading the engine. For cruisers where there’s more power and torque relative to hull displacement the 2.64:1 ahead ratio may be the better way to go. The SD50/60 (pictured) saildrive option has the same 2.32:1 ratio ahead and astern and blows out the engine/drive combo to 213kg. For heavier displacement cruisers or cruising yachts with shallower prop shaft angles, the straight output KM35A gearbox has 2.36:1 or 2.61:1 ratios ahead and 3.16:1 astern.

This choice of gear ratios has long been a Yanmar feature that other marine engine manufacturers should adopt!

Standard is the B panel with key switch (keyless is optional) that has oil pressure and coolant temperature gauges, plus audible alarms for low oil pressure, high coolant temperature and low battery charge. The tachometer has a digital hour-meter, but being rated to 5000rpm when the engine only revs to 3000 annoys my pedantic nature. Surely Yanmar could redesign the dial to read to only 4000rpm.



Since its introduction the Yanmar 3JH5E has been a reliable boat engine, though it pays to shop around when considering buying one as prices can vary greatly from dealer to dealer.

While it’s not as smooth running as the four-cylinder competition and is heavier and bulkier, the Yanmar 3JH5E is completely under-stressed and with regular maintenance should last a lifetime. Fitted with the SD50 saildrive twins it would be capable of powering cats to at least 13.5m or in shaftdrive single unit form a monohull cruising yacht to 11.5m. Alternatively it would suit displacement cruisers to 7m. It will even help reduce flab when idling. And the Yanmar name means very good resale value when it comes time to sell or repower a boat.

For more on the Yanmar 3JH5E, email:



Torque and fuel consumption



BHP (absorbed by prop)












12.1 2.6






















*My recommended minimum and maximum cruising rpm. Yanmar states 2900rpm is maximum continuous but in my opinion, this is too high for constant usage. BHP is brake horsepower, not the weird MHP or metric horsepower that is a contradiction in terms.



YANMAR 3JH5E price: Check with your dealer

TYPE Three-cylinder naturally aspirated diesel marine engine

RATED BHP 37.5 at 3000rpm

MAX TORQUE 115Nm at 1800rpm


BORE x STROKE 88 x 90mm

WEIGHT 186kg (dry w/gearbox)


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See the full version of this review in Trade-A-Boat #251, March / April 2015. Why not subscribe today?

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