Old Faithful: Talking Torque with Andrew Norton

Andrew Norton — 11 April 2019

Throughout its long history the 5.9 has been steadily upgraded from naturally aspirated to turbo-intercooled, electronically managed common rail versions. Currently the peak output is 472 brake horsepower (bhp) or 479 metric horsepower (mhp) at 3400rpm and yet developing this the engine is still reliable. 

A de-rated version of this engine develops 425mhp and is used in single installations to power trawler yachts such as the semi-planing Beneteau Swift 34, which – at 8.2t displacement – can reach 20.7kt at 3100rpm using 71.5L/h and cruise continuously at 14.7kt and 2500rpm using a reasonable 43.1L/h.

But despite the peak output of 472bhp the maximum torque output is 1278 Newton metres, only 14 per cent higher than the long-running 330 model, for years the standard power in the Caribbean 35. The 330 is almost the bottom of the recreational turbo-intercooled electronically managed engine outputs for this engine, so with regular maintenance this engine should survive thousands of hours of usage before needing any serious repairs. The beauty of electronic engine management is that the instrumentation displays real time fuel flow, range to empty and electronic twin engine synchronisation makes evening up the rpm way easier. 

The Nitty Gritty

The 330 has traditional Cummins engineering, such as two valves per cylinder (the common rail models have four valves) and a gear driven camshaft actuating the valves via push rods. 

A simple and time-proven design that should last a lifetime. The 5.9 is a genuine Cummins design, whereas the 6.7-litre engine used by other engine manufacturers is actually an Italian Iveco engine that has some engineering design issues.

Rated to a total of 500 running hours per year with up to 12.5 per cent at Wide Open Throttle, the 330 develops maximum power at a lazy 2800rpm and maximum continuous rpm of 2500, the same as the 425. The thermostat opens at 74 degrees with the designed coolant temperature of 80 to 85 degrees ensuring a long cylinder head gasket life. The relatively low exhaust gas temperature of 567 degrees means that rubber through-hull exhaust pipe fittings aren't stressed when used raw water is injected into the exhaust system.

The raw water pump is gear driven and the impeller is beefy, but check for corrosion around the drive shaft bearing. If corrosion is excessive the shaft can snap leaving the engine with no raw water cooling for the heat exchanger. Also, because the exhaust system is raw water cooled, shaft failure can quickly cause the engine to overheat.

As the 330 is not handed port and starboard, in the Caribbean 35 accessing the port side of the port engine requires removing the dinette, which according to owners takes around 15 minutes. However the port engine has an extended engine oil dipstick checked from above the rocker cover. Gearbox oil dipsticks are easily checked for both, as are the coolant overflow tanks at the forward of the engines.

Depending on how frequently the engines are used I suggest changing the engine oil and filter every 100 to 200 running hours and using a mineral-based diesel-specific SAE15W40 oil, which suits tropical as well as temperate climates. I know that frequency may seem excessive but engine oil and filters are cheap insurance compared to the costs of rebuilding an engine.

The starter motors are mounted reasonably high with the alternators at rocker level, well away from any water in the bilge. 

On the Water

Twin 330s fitted in a mate's Caribbean 35 provided good planing performance but did have to overcome this hull's lack of lift aft. The reason for this is the planing strakes end too far forward, leaving the aft end of the hull with straight deep V surfaces that simply “suck” down the hull despite the inboard engines having a shaft angle of around 12 degrees. Most deep V planing hulls continue at least one strake per side right to the transom, but not the 35. The lack of lift aft is not helped by later 35 having a fuller hull forward than the original Bertram 35, which creates more load on the aft planing surfaces from the slight hull imbalance. The hull should have modified aft with the outermost strake carried through to the transom.

In fact, the 35 is a harder hull to plane than the old Cresta 32 (despite this having V-drive engines) and this was shown by the 330s not cleanly planing the 35 until the rpm was well above where maximum torque is produced. Never a good thing for planing fuel efficiency. When testing any planing hull during performance trials I don't use the trim tabs as a well designed and balanced hull should never need these to plane.

Having offended Caribbean owners everywhere, the 330s did a great job of overcoming hull deficiency. Despite having 1700 hours on the clock they started instantly cold with no smoke of any colour appearing. The electronically-shifted gearboxes barely clunked in and out of gear and when idling with the engine hatches closed the noise level was a mere 65.9 decibels for both engines at three metres. 

The 1.8:1 reduction ratios combined with the 21 x 27 inch four bladed clover leaf props gave plenty of low speed bite and allowed for the one ahead/one astern technique to spin the hull in its own length. However going astern with the rudders straight ahead the hull did have a tendency to wander, corrected by increasing rpm slightly on one engine. 

Coming out of the hole no smoke was apparent and the best planing fuel efficiency was between 2100 and 2500rpm. Through tight turns at 2250rpm the hull maintained a clean plane and the engines held their rpm without touching the throttles. Obviously intended to hold a clean plane in rougher water the clover leaf props did reduce WOT speed and there was some “drumming” from blade turbulence impacting on the hull bottom. Still, the 35 is more about offshore cruising than WOT performance.

The only times we used the trim tabs were across the wind to compensate for the hull leaning into the wind and for the 405-litre water tank opposite from the 7 kVA Onan genset as the tank was only half full. I'll never understand why the genset wasn't mounted on the centreline along with the water tank. I realise access to the offset genset is better because of the sunken galley to port but surely the genset could have been mounted in another location.

Still the day was about the engines and not the hull, which despite its design faults has one of the best accommodation layouts I've ever seen in a 35 foot cruiser. The engines performed flawlessly with plenty of bottom end torque and no real indication of their trucking heritage.

The Wrap

I really like the combination of traditional diesel engineering with electronic management. Though being a diesel the 330 may still suffer from cylinder bore glazing if used for extended idling periods, the possibility of this happening is way less than a mechanically injected engine. And having no black soot on the transom is very nice. 

Spare parts for the 5.9 in remote areas should never be a problem as the engine has been around for so long.

For the location of your nearest Cummins dealer go to cummins.com.au.


Cummins QSB 5.9 – 330

Engine Type Straight six turbo inter cooled direct injection diesel 

Rated BHP/MHP* 325.7/330.4 at 2800rpm

Max Torque 1125NM at 1800rpm

Displacement 5875cc

Bore x Stroke 102 × 120mm

Dry Weights 712kg

* Brake horsepower/metric horsepower or PS.


Outback Travel Engine Motor Adventure Ocean Water Safety Cummins

External Links