Cummins 330S marine diesel engine review

The Cummins QSB5.9 – 330 marine diesel engine should provide thousands of hours of operation with the right maintenance.

My mate Chris grew up in a trucking family and over the years I’ve known him he has told me that of all the brands of trucks owned those powered by Cummins diesels were always the most reliable.

So it was a no-brainer for choice when he upgraded from his Yanmar-powered Cresta 32 to a Caribbean 35. The standard electronically-managed QSB5.9 – 330 marine diesel engines were exactly what he wanted. Instead of the mechanically-injected Yanmars he now had fuel flow at his fingertips, plus range to empty, synchronisation of the engines while using just one of the single throttle levers and electronic gearbox shifting. Yet the engines retained traditional truck engineering such as OHV with gear-driven pushrods and a heavier-duty cycle.

Whereas the Yanmar marine diesels were rated to no more than 250 hours of usage, the Cummins are rated to 500 hours a year with one hour in eight at WOT. They develop max power and torque at much lower rpm and spares are cheaper and easier to source.

Cummins 330S marine diesel engine

The QSB5.9 – 330 is less than halfway up the range of outputs Cummins offers for this engine. The 5.9 can develop up to 472bhp or 479mhp at 3400rpm, so with regular maintenance the 330 should provide thousands of trouble-free running hours.

The turbocharged straight-six has seawater cooled aftercooling to provide maximum cool combustion chamber air charge and is designed to run at around 80 to 85°C with the thermostat opening at 74°C. The max exhaust manifold outlet temperature of 567°C is reasonably low, as is the 17.2:1 compression ratio.

Mounted in the Caribbean the engines are not handed so some service items on the port engine are a little hard to reach without removing the dinette. Still the standard two-hatch access is adequate and the port engine’s oil dipstick is mounted on top so the level can be checked without too much of a reach.

The oil dipsticks for the Twin Disc hydraulic gearboxes are easily reached and sensibly International Marine mounts the coolant overflow tanks at the forward end of the two-hatch access. The starter motors are mounted reasonably high with the alternators at rocker cover level. These are supplemented by a 1500rpm 7kVa Onan genset for the air-con and all-electric galley, so no LPG aboard this boat!

Depending on how often they are used I’d change the oil and filters every 100 to 200 engine hours or annually. I suggest using a specific diesel mineral-based SAE 15W40 oil.

Cummins 330S performance

Chris’s near-new but frequently-used Cummins engines had 1700 hours on the clock when I tested them in June, but the only time there was an exhaust smell was when backing up hard or aggressively using the one ahead/one astern manoeuvring technique. The reduction ratio of 1.8:1 and the 21 x 27in four-blade props gave plenty of “bite” in tight confines, but in my opinion the clover-leaf blade design did limit planing speeds.

Idling out from the mooring with hatches removed the decibel reading at 3m was 66.1 for one engine and 70.2 for both. With hatches closed the reading for both was 65.9dB, damned low for diesels of this output. There was hardly any vibration in the hull when idling in gear. The Caribbean 35 is fitted with trim tabs but as International doesn’t fit tab-angle gauges we tested the engines with the tabs up.

There was no diesel smoke from fuel oversupply coming out of the hole, but the 35 didn’t plane as easily as expected and I think the QSB5.9 – 380s would be better as the efficient planing zone is only from 2100 to 2500rpm. With full fuel and water and Chris and myself aboard, total displacement was 10.2 tonnes, a fair old load for the 330s to handle.

Through tight turns at 2100 to 2500rpm the revs held with no evidence of overloading. In fact the engines were slightly under-propped, which is always sensible in a planing hull. From 2100rpm upwards there was a slight drumming aft, most likely from the prop blades being so close together, but not enough to be annoying or reduce my copious flab!

The Trade-a-Boat verdict

Chris is now in seventh heaven with his Cummins-powered Caribbean 35. He now owns the boat he’s long wanted and with the right engines. Chris and wife Fran bought the boat on the Gold Coast and fully know how to handle it from the voyage in very rough conditions back to Lake Macquarie, NSW.

For more on the QSB5.9 – 330 marine diesel engine, contact Cummins South Pacific on 0800 286 646 or visit cummins.co.nz.

Performance: twin 326hp Cummins QSB5.9 – 330 marine diesel engines.

Twin 326hp Cummins QSB5.9 – 330s. Average of two-way runs on Lake Macquarie-NSW using Raymarine GPS, Cummins Marine fuel-flow gauges and a handheld decibel meter; calm water

RPM	SPEED (KTS)	FUEL BURN (LT/H)	RANGE (LT/NM)	dB (3M)
600	5	3.6	0.7	65.9
750	6.1	6.4	1	73.8
1000	7.5	10.6	1.4	79.7
1250	8.6	17.1	2	83.2
1500	9.5	32.6	3.4	86.7
1750	11.5	51.2	4.5	86.8
2000	16	68.6	4.3	86.2
2100	18	72.9	4.1	86.1*
2250	19.5	83.2	4.3	87.1
2500	25	97	3.9	88.2
2850	29.5	122	4.1	90

* Note noise level lower at 2100rpm than at 1750 to 2000rpm because of hull fully planing and less engine load. The best planing efficiency zone was at 2500rpm, also the maximum continuous rpm. Fuel burn figures combined for both engines. Sea-trial data supplied by the author.