Volvo Penta D2-75 marine diesel engine

Back in the early 90s, car manufacturers looked for ways of increasing diesel engine output while using the same base power head. Mitsubishi, for example, fitted straight turbocharging to the Triton’s long-running 2.5-litre 4D56 diesel that increased power by a modest 13 per cent but torque at the same rpm by a useful 27 per cent over its naturally aspirated counterpart.

Mitsubishi continued this theme with the 2.8L 4M40 diesel fitted to the ’94 Pajero. But it went one further by also fitting an intercooler that reduced the temperature of the air being force-fed by the turbo, increasing its density. The results were a 30 per cent power increase but a whopping 47 per cent improvement in torque, again at the same rpm as the naturally-aspirated engine.

Back to the Volvo Penta D2-75 marine diesel engine – this mechanically injected indirect injection unit uses the same base engine as the Volvo Penta D2-55 but develops 34 per cent more power with a 57 per cent higher torque output — but unusually the latter peaks at much lower rpm.

Volvo Penta D2-75

There’s no doubt the Volvo Penta D2-75 marine diesel is aimed at light displacement racing yachts and semi-displacement cruisers and in my opinion should not be installed in heavy displacement cruising yachts. The fuel efficiency is very good up to 2600rpm but the last 400rpm really suck down the juice, resulting in 43 per cent higher fuel flow at wide-open throttle than the Volvo Penta D2-55 while the torque falls off substantially, indicating Volvo has really stretched the output limits of the D2-55 engine.

In comparison, a similar-displacement direct injection competitor produces four per cent more torque at the same rpm but uses seven per cent less fuel at WOT for the same power output. The reason is that while indirect injection makes for very low exhaust emissions, because the fuel and air are mixed thoroughly in the pre-combustion chamber, this convoluted route to the main combustion chamber reduces power and torque outputs for a given piston displacement.

So why would you buy a Volvo Penta D2-75 marine diesel? Well, it has the same footprint as the D2-55 and is the same overall length as the D2-55 because the turbo is mounted above the gearbox, and despite its increased power and torque the shaftdrive version is a mere six per cent heavier. The Volvo Penta D2-75 marine diesel is also available with a sail drive for racing yachts where the engine may be mounted forward or aft of the leg.

Apart from the turbocharger and after cooler, the Volvo Penta D2-75 marine diesel has the same features as its buddy. There’s a maximum running heel of 35 degrees port or starboard so the engine can be started while the yacht is heeled over under sail. The voltage-regulated alternator produces up to 115 amps, with 35A available at the 850rpm idle. Both top and side-mounted oil fillers are provided and all main servicing points such as the fuel filter/sedimenter, raw and fresh circulating water pumps and alternator are at the forward end of the engine.

The turbocharger and exhaust manifold are fresh-water cooled to reduce condensation build-up during extended periods of disuse and the heat exchanger cooling with 95-degree fully opened thermostat allows the engine to run hot to reduce sump oil dilution during periods of low-load operation.

Engine maintenance

As with the D2-55, I’d use either a diesel-specific SAE 10W30 or SAE 15W40 oil depending on the ambient temperature range, and I’d change the oil and filter every 100 hours or six months.

After a long run the engine should be allowed to idle for a couple of minutes before switching off to allow the turbocharger to spool down. Remember: if the engine is quickly switched off after a run, the turbocharger bearings will still be rotating at upwards of 50,000rpm but will be starved of oil.

I also recommend warming a cold engine for around five minutes at low revs before opening out the throttle. This ensures the turbocharger bearings are well lubricated before coming under load.

See more Volvo marine diesel reviews

Gearbox options

The same gearbox options as the D2-55 are available, with either eight-degree down angle at the output flange or straight output, all with clockwise or counter-clockwise output rotation for twin installations. The down-angle ’box would be better for yachts and displacement cruisers because the engine could be mounted parallel to the waterline but most owners of racing yachts will opt for the sail drive, which has cooling water intakes located well up the leg and allows for a very compact installation.

With the mechanical MS25A ’box the D2-75 is 915mm long, 545mm wide and 693mm high while on its fibreglass mounting bed the sail-drive version is 1036mm x 600mm (approx) x 799mm.

The Trade-a-Boat verdict

Volvo Penta has done a good job of extracting substantially more power and torque from the D2-55 without significantly increasing weight. Like all turbocharged diesels it has to be treated more carefully and should be slightly under-propped to allow it to reach a touch over its rated rpm. But it still has all the design features of the D2-55 that reflect Volvo’s long experience in building yacht diesels. And at low rpm there will still be enough vibration through a fibreglass hull to gently melt away body flab.

Call Volvo Penta Australia on (07) 3726 1500 or visit Volvo Penta Australia for more information.

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Volvo Penta D2-75 sea trials

Volvo Penta D2-75 specs

Engine type Four cylinder indirect injection turbocharged marine diesel engine

Rated BHP/MHP* 71.0/72.1 at 3000rpm (propshaft)

                                73.7/74.8 at 3000rpm (crankshaft)

Max torque 212.2Nm at 1800rpm

Displacement 2216cc

Bore x stroke 84x100mm

Weight 258kg (dry w/gear box)

             264kg (dry w/sail drive)

*Brake horsepower/metric horsepower