MERCURY MARINE REVAMPS MERCRUISER ENGINE FOR BOATS

Mercury's latest inboard sets new standards in marine engines

Mercury Marine’s new 4.5L 250-hp MerCruiser engine is the company’s latest development in inboard marinization. This 4.5L V6, designed and built in-house, is being pitched as an alternative to the 260-hp 5.0L V8 and won’t be found in any automobiles. The MerCruiser was designed from the ground up and exclusively for marine use, unlike other engines that currently dominate the sterndrive and gas inboard market. The small-block style engine features a cast iron block, pushrod valve actuation, and two valves per cylinder. The aluminum cylinder heads and intake manifold are cast by Mercury in its own foundry, with an outside supplier casting the iron block. Bore and stroke are 4.0 x 3.6 inches (101 x 92mm). The option of raw-water or fresh-water cooling will be offered with the engine, which is compatible with MerCruiser Alpha and Bravo One/Two/Three outdrives, and can be configured with cable or SmartCraft DTS controls. Joystick piloting for twin-engine installations comes with the DTS option.

The 4.5 weighs 940 pounds in its lightest configuration (raw-water cooled with an Alpha drive) and is about four inches shorter in length than the 5.0L. Boat builders willing to alter the interior of their boats can also gain four inches of cockpit space with the 4.5L package. The WOT range of the 4.5L is 4800 to 5200 rpm. Though its torque curve is broader and flatter than that of the V8, the 4.5L makes less peak torque than the 5.0 thanks to an intricate scroll-type intake manifold cast with the lost foam process. The intake manifold was designed to place the throttle body facing aft so that intake sound – the muffling of which is restricted by the US Coast Guard – issues away from the cockpit. Other features such as new engine mounts and the rigid structure of the cast-aluminum oil pan also help to reduce noise, with a special lightweight flywheel reducing the “clunk” heard when shifting into gear. Mercury also claims that the engine’s new water pump is smaller, stronger, self-draining and more efficient overall than previous designs.

The arrangement of key consumer “touch points” on a bar in the upper front of the engine for the dip stick, oil filter, oil fill and power steering fill is another marine-specific feature of the 4.5L. A detailed service label with a QR code also allows the viewing of maintenance how-to videos on smart phones. This engine does not require a traditional 20-hour service either, with the valve train being maintenance-free. The 4.5L has the same air-pressure drain system found on the MerCruiser 350 MAG, allowing the owner to clear most of the water from the engine to extend service at the end of the season when freezing temperatures might occur. The new MerCruiser 4.5L will cost boat builders about the same at the 5.0L V8. Consumers can expect Mercury to offer a de-tuned version of the 4.5L as a replacement for the 220-hp 4.3L V6 in the future.