Review: Mercury 40 LW outboard motor

By: Andrew Norton

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  • Trade-A-Boat

Gutsy, simple and easy to start — that best describes the 40hp Mercury 40LW outboard motor.

Review: Mercury 40 LW outboard motor
The Mercury 40LW outboard motor is easy to maintain and is not overly complicated.


Originally published in TrailerBoat #284, July / August, 2012.

It’s a sad fact of life that I’m not as strong as I used to be. When I was young I had no trouble starting twin-cylinder outboards up to 40hp. But that was almost 20 years ago and now I have trouble pulling the skin off a rice pudding.

For me, engines such as the Yamaha Enduro 40 and Suzuki DT40 (which are superb engines for open tinnies) are a bit challenging on my flabby arms. I prefer three-cylinder engines, where the third cylinder provides sufficient engine balance to achieve cranking speed, like the Mercury 40hp LW outboard.



Since its Aussie introduction more than 20 years ago, this engine has been steadily improved through combustion chamber design modifications to make it perform better and use less fuel. When I first tried a Mercury 40LW more than a decade ago it was easy to start and had plenty of grunt, but it was a little "chuggy" when idling. But not so the current model I tested in May, which was beautifully smooth across its entire rev range, with only a slight hesitation on transition from the idle to main carbie jets.

The Mercury 40LW outboard develops 39.9hp at 5000rpm with a wide open throttle (WOT) range of 4500 to 5500rpm. The three-carburettor, loop-charged, 697cc powerhead has "Modular CD" ignition for smoother running.

An 11amp alternator is optional and the gear ratio is 1.85:1. The dry weight in manual start longshaft form is 71kg. Mercury Marine recommends servicing the 40LW every 100 hours or annually after the first service at 20 hours. Providing servicing is performed by an authorised Mercury service centre, the recreational-usage warranty is five years — the best of all the carbie two-strokes.



Mounted on a polyethylene Kiwi-built Smartwave 4800 open dinghy and swinging the standard 11in-pitch alloy prop, the demo 40LW was perfectly matched to the hefty hull, which displaced 650kg with two adults aboard.

The only drama was that the transom design wouldn’t allow the trim pin position to be altered when the outboard was mounted on the transom. This meant we were stuck with the second trim position, which limited planing speeds. I would have preferred to use the third position on this hull, but that’s life! Also, the reverse lock release lever should flip up instead of down to simplify tilting the engine when coming into the ramp.

However, the engine started easily hot or cold with a firm two-handed pull and despite running on a 25:1 break-in mix instead of the normal 50:1 mix, it blew oil smoke only below fast idle. When trolling the vibration levels were on par with the Yamaha 40V and way less than the Enduro 40 or DT40.

The Mercury 40LW outboard planed us easily at a one-third throttle opening and accelerated hard from half-throttle upwards. Although a tachometer wasn’t connected I was able to work out the rpm due to various prop slip formulae and having previously tested a 40LW with fuel flow gear, I estimate I had a fair idea of fuel consumption at the various throttle openings.

From my past experience with long-term testing engines like the Mercury 40LW outboard, the average fuel consumption should be around 5lt/h, so this engine is not expensive to run. The standard portable fuel tank holds 25lt — more than enough for a day’s angling.


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Fortunately Australia doesn’t have compulsory outboard exhaust emission regulations as our poor mates across the Pacific do, so engines like the 40LW will still be sold here for some time to come. Despite the howls from greenies, that’s a good thing because it allows more budget-conscious anglers to get to their favourite fishing spots on our beautiful waterways, without needing to re-mortgage the house. The review Mercury 40LW outboard was supplied by Lifestyle Marine for Toronto in NSW (tel: (02) 4959 1444) and as of June 2012 it had a price of $4300 RRP, with a spare alloy prop costing only $120.



For anglers after a simple, manual-start outboard for larger open tinnies and hulls like the Smartwave 4800, the Mercury 40LW outboard motor is very hard to pass up. It’s what I call an "honest" engine, one that does everything it was designed to do well while remaining straightforward to maintain and service. Really, the only complication concerns the three carbies, but unlike multi-carbie four-stroke outboards, should the Mercury 40LW engine carbies go slightly out of tune the performance and fuel consumption won’t suffer greatly.

The review Mercury 40LW appeared well built with the typical high quality Mercury paintwork.



With two adults, pushing 650kg in total.



2.3kts (4.3kmh)

800rpm (trolling)

12.1kts (22.5kmh)

3300rpm (clean plane, 1/3 throttle)

19.7kts (36.5kmh)

5000rpm (cruise, 3/4 throttle)

24.6kts (45.7kmh)

5700rpm (wide open throttle)




Tohatsu M40D

Yamaha 40V
















OEDA Stars



* Includes hydraulically-assisted tilting.

Originally published in TrailerBoat #284, July / August, 2012. Why not subscribe today?


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