For the longest time, Mercury has been taking automotive engines and “marinizing” them for use in inboard and stern-drive applications. They were and are most often Chevrolet engines, and the urban legend has long been that GM has enough manufacturing capacity to make all the engines the marine industry needs in just one day.
There was and still is nothing wrong with that production model, and it has resulted in everything from trusty V6’s in family runabouts to fire-breathing big-block V8’s in high-performance offshore V-bottoms and catamarans.
In the marketplace of trailer-sized boats, the V6 of choice for decades has been the MerCruiser — and Volvo Penta — 4.3-liter V6. They usually are rated for about 220 horsepower and they have proven to be reliable performers.
However, Mercury has released something you will soon be seeing in the used-boat market: the MerCruiser 4.5 liter V6. So, if you see one in an ad for a new or used boat, it’s not a typo. This is not a Chevrolet engine or a power plant from any other automotive manufacturer, but a proprietary V6 designed, cast, and built by Mercury — and it is superior to the 4.3 in every way.
First, it makes more power. At 250 horsepower, the MerCruiser 4.5-liter is nearly on par with some of the lower-end V8s. Second, it does so with two fewer cylinders, so it’s more economical. It also weighs less, which is important to fuel economy. And, again, it has been designed from scratch to be a boat engine.
It has a couple of nifty features that are unique to boating. For example, it comes with adaptive speed control, which automatically maintains engine rpm regardless of load or water conditions. It also has some features to make maintenance easier, such as a front-mounted drive-lube monitor, an easy-to-reach oil filter and — get this — labels with QR code links to how-to videos that can be accessed via smart phone.
I had the pleasure of driving a 20-foot runabout with this engine, and it is remarkably improved over the GM V6. It’ll be at least a year or two before boats with these engines start showing up the used market, but if you’re given a choice between it and the old 4.3, go with the 4.5.