Review: Yanmar 4JH5E Marine Diesel Engine

Direct injection diesel engines have rapidly overtaken indirect-injection diesels in the automotive industry. And with good reason — they develop way more power and torque than their same-displacement indirect competition, yet deliver better fuel efficiency.

With direct injection, fuel is injected directly into the combustion chambers – no stuffing around with pre-combustion chambers to thoroughly ignite the fuel before it reaches the combustion chambers. Trouble was that old direct-injection diesels never burnt their fuel completely, resulting in higher exhaust emissions unless the engines were turbocharged. Blowing air in under pressure creates a better air/fuel mix and reduces emissions.

The Yanmar 4JH5E is one such example. It’s Yanmar’s most powerful naturally aspirated recreational marine diesel engine and develops heaps more torque than the indirect competition, yet complies with EU and US exhaust emission regulations.

Yanmar 4JH5E marine diesel

There is no flimsy engineering on the Yanmar 4JH5E marine engine. It has a gear-driven camshaft that operates push rods for the eight overhead valves and a cast iron cylinder head and block. The engine has a crossflow head, with the exhaust manifold to port and a relatively low-pressure inline fuel injection pump to starboard.

The Yanmar 4JH5E marine diesel is in essence a four-cylinder version of Yanmar’s three-cylinder 3JH5E. Adding another pot increased the engine/gearbox weight by 15 per cent but the maximum power is 38 per cent higher and torque is 35 per cent greater – and at lower rpm. As is the case with most four-cylinder diesels versus their triple counterparts, the substantially lower vibration is not only kinder to accumulated flab but also your hull if of timber construction.

Of course, heat exchanger cooling on the Yanmar 4JH5E marine engine is standard, as is an 80-amp voltage-regulated alternator. That’s a bit light for an engine of this output but Yanmar offers a choice of additional 80 or 130A alternators that mount on the starboard side of the engine. There’s even a shroud over the drive belt for the alternator and fresh water circulating pump so perhaps the Japanese aren’t as confident as European manufacturers that owners will keep their fingers away from the belt. The seawater pump is gear driven and accessed just below and to port of the shroud.

What I really like about this engine is that it’s not too powerful to run Yanmar’s mechanical cone clutch gearboxes, with either straight or seven-degree down angle outputs. These have a deeper gear reduction in reverse than forward, which means that going astern, when an engine is under more load than going ahead, the deeper reverse reduction reduces engine loading and allows the torque band to be reached faster. It’s indicative of Yanmar’s understanding of what owners of displacement hull boats need and to my knowledge no other recreational marine diesel manufacturer offers this type of gearbox despite the concept being around at least 40 years. 

The straight-output ratios are 2.36 or 2.61:1 ahead and 3.16:1 astern, or 2.33 and 2.64:1 ahead and 3.04:1 astern for the down-angle ’box. The deeper ratios ahead would suit a heavy displacement cruising yacht, with the taller ratios more for racing yachts or cruisers that have better power to weight ratios. Being mechanical, all these ’boxes can handle a free-wheeling prop under sail if a folding prop is not fitted.

The additional pot adds 95mm to the overall length compared with the 3JH5E, the dimensions being 871mm long, with the same 560mm width and 623mm height. Yanmar recommends diesel-specific SAE 10W30 oil for cooler climates and SAE 15W40 oil in tropical conditions and I suggest changing oil and filter every 200 hours or annually – or every six months if the engine is used infrequently.

Two instrument panels are available but if your budget allows, the digital C panel with analogue tachometer (incorporating digital hour meter), coolant temperature and oil pressure gauges plus audible alarms would be the way to go. There’s also a choice of key or keyless starting. The only annoying feature of this panel is that the tacho runs to 5000rpm while the engine will only reach 3000rpm.

The Trade-a-Boat verdict

As with the 3JH5E, Yanmar has clearly shown it knows how to build a marine diesel. The Yanmar 4JH5E has heaps of bottom-end torque with relatively low fuel consumption in a package that’s substantially lighter than some of the same-output indirect injection competition. Its ability to meet EU and US exhaust emission regulations means that it won’t blow black smoke all over your transom or into the cockpit in a following sea as older direct injection diesels did, and when you’re voyaging to remote areas it’s comforting to know that parts should be available when you need them.

Yanmar 4JH5E specs

Engine type Four cylinder direct injection marine diesel engine

Rated BHP/MHP* 53.1/53.8 at 3000rpm at crankshaft

Max torque 155Nm at 1600rpm

Displacement 2190cc

Bore x stroke 88 x 90mm

Weight 213kg (dry w/gearbox)

* Brake horsepower/metric horsepower