Diesel Lite

Cummins MerCruiser's new 4.2 ES 300 diesel stern drive.

Thanks to the efforts of several engine manufacturers, your engine choices are greater than ever. The stern drive market, for instance, was once the exclusive domain of gas-powered engines. No more. For those who want the dependability, longevity, and safety of a diesel combined with the easy handling and performance of a stern drive, the new 300-bhp diesel from Cummins MerCruiser meets both requirements. The 4.2 ES 300, a turbocharged in-line-6 engine with 254 cid, provides the snappy performance you’d expect from a stern drive application.

In test runs on several boats, the 4.2 ES 300 displayed good acceleration out of the hole and offered plenty of midrange torque-traits you’d expect from a gasoline stern drive. This engine puts out more ambient noise than an equivalent gasoline stern drive, but still, it’s considerably less than what you’d hear on a conventional diesel.

Cummins MerCruiser boasts that the motor leaves virtually no smoke in its wake, a claim I verified in person at the manufacturer’s assembly plant. Two-stage direct injectors and spiral-shaped intake ports contribute to the clean burn as well as to good fuel economy-the engine burns 10 gph at 2600 rpm and maxes out at 13 gph at 3800 rpm.


Compared to Volvo Penta’s D6 310 (Motorhead, May), the 4.2 ES 300 puts out 10 fewer horses but weighs 357 less with the Bravo Three drive. The Volvo rates 5.3 pounds per horsepower (pph) whereas the 4.2 ES 300 rates 4.3 pph. Although the 4.2 ES 300’s 254 cid is significantly smaller than the Volvo D6 310’s 336 cid, both spool up to nearly 4000 rpm at top end. The third player in the lightweight diesel stern drive market, the Yanmar 6LSTZE, is a 254 cid in-line-6 that generates 315-bhp at 3800 rpm and features direct injection. The Yanmar will fit in a more compact engine compartment than the 4.2 ES 300. The Yanmar burns less fuel at 2600 rpm (7 gph) but more at WOT (15 gph).

The 4.2 ES 300 works with DieselView, Cummins MerCruiser’s version of Mercury’s popular SmartCraft system. The Common Area Network (CAN) display gives you throttle, gear pressure, and temperature data at the helm as well as fuel burn and engine hours, and it provides such neat services as reminding you when it’s time to change the oil. You can toggle through these functions on a dash-mounted display about the size of a typical depthfinder. MerCruiser beefs up the outdrives for this diesel package with a heavy-duty U-joint, stronger thrust bearings, and a thicker upper gear floor, among other features designed to handle the extra torque. Contact Cummins Mercruiser Diesel; 800/343-7357


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