Suzuki DT30 outboard engine review

When I first tested a Suzuki DT30 outboard motor way back in 1982 on a 4m Quintrex, I was impressed with its performance and fuel efficiency. Of course, having a loop-charged powerhead it was nowhere near as smooth as the old cross-flow Johnson 30 outboard, but back then I was way fitter and not looking for a workout through transmitted engine vibration.

Those were simpler times, when oil injection was considered sophisticated and there was only one manufacturer of four-stroke outboard motors on the Aussie market. But of the 30hp outboard engines, the Suzuki DT30 stood out. Not only did it outperform the 521cc Johnson engine, it also used around 20 per cent less fuel. And it all came down to a combination of loop-charging and piston displacement.

SUZUKI OUTBOARDS

By using slightly domed pistons instead of those with a ridged top (as found in cross-flow engines) the pistons can be made lighter, reducing the flywheel size and the power needed to drive it. This is why at higher revs most loop-charged engines outperform their cross-flow counterparts. At 499cc the twin-cylinder DT30 still has the largest displacement of any carbie two-stroke 30 and while it doesn't develop any more power than the competition, it produces way more torque.

Developing 29.6hp at 5300rpm with a Wide Open Throttle rev range of 5000-5600rpm it's an under-stressed unit, while its main and auxiliary cooling water intakes ensure the powerhead is never likely to suffer from water starvation. The single carbie is easy to maintain and there's a simple mechanical ignition timing advance. The gear ratio is 2.09:1 and the manual longshaft model weighs 57.5kg, with electric start adding 4kg. A 6A alternator is optional, but as it doesn't have voltage regulation only a car battery should be used to prevent frying it on longer runs.

To give the impression of recent engineering, over the years Suzuki has swapped the fuel / oil ratio from 50:1 to 100:1, also fitting an front gearshift to complement the rounded upper cowl.

Rather coyly, Suzuki hasn't undertaken emissions testing to gain an OEDA star rating for this engine, but based on its design and stats it would probably rate as "1 Star". Powerhead access is excellent and servicing is recommended every 100 hours or annually after the first 20 hours. The recreational-usage warranty is two years.

PERFORMANCE

In recent history I tested a DT30 on a Blue Fin 4.2 Mangrove Jack - a vee-noser - and it performed just as well. A firm two-handed pull was needed to start the engine manually but the electric starter was a nice touch, and despite running on a 25:1 break-in mix oil smoke appeared only below 2000rpm. When trolling the vibration levels were acceptable and the upfront shift was far easier to use compared to reaching around the upper cowl to access the old side shift.

Slightly underpropped to handle heavier loads and swinging a 12in-pitch alloy prop, it easily planed our 470kg payload at roughly a two-thirds throttle opening, with no prop ventilation occurring through tight turns at 4000rpm. Of course, like all carbie two-strokes it was fairly raucous at or near WOT but still not loud enough to hamper conversation.

THE VERDICT

I can't keep using the word "honest" to describe simple engines like the DT30. Well, how about "practical" for saltwater anglers? It's simple to maintain and service and with just a little TLC should give years of reliable service, although saltwater corrosion resistance may be another matter.

It has plenty of poke for tinnies to 4.3m and because the gearcase ratio is not too deep there's no real prop steer torque to speak of, while above 2000rpm it vibrates little more than a three-cylinder outboard.

As of January 2013 the manual longshaft Suzuki DT30 price was  $3058 and the electric-start model price was $3456. A spare alloy propeller cost around $240. The review Suzuki DT30 outboard motor was supplied by the Haines Group, (07) 3271 4400.

ENGINE ECONOMY

2.2kts (4.1kmh) @ 780rpm (trolling) - 1.2lt/h

11.6kts (21.5kmh) @ 3600rpm (min. plane) - 7.5lt/h

16.1kts (29.8kmh) @ 4000rpm (cruise) - 8.4lt/h

23.1kts (42.9kmh) @ 5690rpm (wide open throttle) - 13.5lt/h

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Originally published in TrailerBoat magazine #293, March 2013.