Yamaha V6 four-stroke outboard engines

By: Andrew Norton

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Yamaha’s new V6 four-strokes provide DFI two-stroke performance, which startled a not easily startled Andrew “Engine Man” Norton.

Yamaha V6 four-stroke outboard engines
The acceleration of the new Yamaha V6 four-stroke outboards is breathtaking. At or near WOT they are much quieter than the DFI competition, and their mid-range fuel efficiency is also ahead.

Originally published in TrailerBoat #263, November / December 2010.

Released in June 2010, Yamaha’s F225F, F250D and F300B outboard motors are the first naturally-aspirated four-stroke engines I’ve reviewed to have similar holeshot performance to the DFI Evinrude E-TEC and Mercury OptiMax competition.

Across the entire rpm range their acceleration is simply breathtaking, yet at or near WOT they are much quieter than the DFI competition, and their mid-range fuel efficiency is also ahead. In fact, the mid-range torque is more akin to comparable-output DFI engines than four-strokes.


YAMAHA F225F / F250D / F300B

According to Yamaha Australia, the 4.2lt powerhead was designed specifically for marine use. It’s also the first Yamaha marine engine to have a plasma fusion coating on the cylinder bore walls instead of the traditional steel liner. Yamaha claims the 10 micron coating is 60 per cent harder than steel and by combining this coating with slim cylinder walls the engine-only weight has been reduced to 126kg.

As with the Yamaha V8 350, the V6 range has full digital electronic control with "fly by wire" control of throttle and shifting. A new "shift damper system" (SDS), to allow the prop hub to slip slightly when forward or reverse gear is selected. This results in an almost imperceptible "clunk" when the dog clutch engages.

To increase cooling system capacity, auxiliary intakes are fitted to the leading edge of the gearcase torpedo, in addition to the main inlets just above the torpedo. And to reduce overheating of the prop hub under load, an exhaust pressure reduction system is fitted, which functions by diverting cooling water from the impeller back to the exhaust passages. This also improves exhaust gas scavenging.

Another advantage over the direct competition is the 70amp alternator, which still produces 55amp at 1000rpm and has a 50amp net or dedicated battery charging capability. And should the alternator be set up to charge two batteries at the same time, the system will always fully charge the starter battery before the house battery.

Like the Yamaha F70A, which was also released this month, the V6 engines have the optional "YCOP" engine immobiliser system with a remote keypad. It uses a standard watch battery that’s easily accessed by removing screws.

The engine starts with a push-button that, once running, will not inadvertently engage the starter motor if you accidentally push it. Like the F70A, this engine has an adjustable trolling rpm control, varying from 600-1000rpm in 50rpm increments. However, operating this system through the Yamaha digital instrumentation is not as straightforward as it could be.



Recommended servicing intervals for the engines are every 100 hours or annually after the first 20 hours. The engines use a single toothed serpentine belt with idler pulley to maintain belt tension for driving the four camshafts. This belt has a 1000-hour designed lifespan. Variable valve timing operates on the intake valves and holds these open longer from 2000rpm out to WOT. As with all Yamaha double OHC or quad-cam engines, the camshafts need to be removed to adjust the bucket and shim valve clearance. However, this is only required every 500 hours and doesn’t require removing the engine powerhead, as is the case with some chain-driven camshaft outboards.

Although the three engines have the same 10.3:1 compression ratio, the 225 and 250 are designed to run on standard 91 RON unleaded while the 300 needs minimum RON 95 premium.

As with the F70A, an anti-knock sensor is fitted should the octane level be below that required. An oxygen sensor is not fitted in the exhaust so using higher octane fuel will not advance the ignition timing and allow the engine to develop more power, as do some automotive engines.

The 225 and 250 can use standard E10 unleaded with up to 10 per cent ethanol but I recommend not using this fuel due to its phase separation problems and solvent properties, particularly in boats with underfloor fuel tanks.



  • Excellent holeshot
  • Very good mid-range
  • Fuel efficiency
  • Electronic shifting




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Originally published in TrailerBoat #263, November / December 2010. Why not subscribe to Trade-a-Boat today?


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