No one can accuse Mercury of rushing its latest outboard — a non-supercharged 150 hp four-stroke — to market. After five years in development and $25 million in research and tooling costs, Mercury unveiled the 150 FourStroke. Heck, the three-piece cowling alone took 19 months to perfect. All Mercury tried to do was to be better in every metric than its competition and make the engine as simple, light and maintenance friendly as possible.
Its 3.0 liters of displacement are the most in the industry for a 150 — even larger than Mercury’s supercharged Verado line of in-line six-cylinder 2.6L engines that produce from 150 to 350 hp. The goal was to have an engine that could produce plenty of power without straining the powertrain, for improved longevity.
Built for the Future
Uncertainty about future environmental regulatory changes makes it difficult to design an engine that can change with the times, but the 150 is well-positioned, being built ready to accept a bolt-on catalytic converter, as is currently mandated for most sterndrive engines. Higher-ethanol fuels are coming, so the 150 is designed to accept up to 20 percent ethanol-spiked gasohol, merely by reflashing its internal computer chip. It’s good to go right now for 10 percent ethanol regular.
You Do It
The 150 FourStroke is designed with do-it-yourselfers in mind. Unhook one latch, slide off the 16-pound cowl and you’re ready to go to work. To change the oil, connect a hose to the drain fitting, and with just a half turn of a crescent wrench, you’re draining. A similar fitting allows you to connect the hose to a drain pan for the oil filter, which features an automotive-style spin-off design. Most people wait too long to change the fuel filter because it can be a hassle, but with the 150 you just grab the oversized yellow handle and pull (every owner-doable maintenance location is yellow). The maintenance schedule is even printed on a panel inside the engine for quick reference. On the “cheat sheet” is a QR code you can scan with your smartphone that will link you to YouTube videos that show how to perform routine maintenance.
Keep It Simple
Mercury decided to build a four-stroke engine that has as few moving parts as possible, so it went with a single overhead cam design that features two valves per cylinder instead of the usual four. That’s not to say it’s low tech; its rocker arms come straight from Formula One racing technology. A single throttle body allows air into the long, tuned pipes, which are made of composite material to keep the overall weight at 455 pounds, the lightest four-stroke 150 on the market. The valve train is considered no-maintenance like all other Mercury FourStrokes, so there’s no need to take it to the shop to have the valves shimmed periodically. A focused mount system is positioned farther away from the powerhead to reduce heat and is angled 45 degrees to cut vibration.
To provide electricity for the vast array of electronics most boats sport these days, there’s a belt-driven, 60-amp, on-demand alternator that only provides power when you need it. Driven by the engine’s serpentine belt, the charging system senses when battery voltage drops below 14.2v before engaging. At idle, the alternator puts out a net charge of 30 amps, and at 3000 rpm it cranks out 46 amps.
We got our first up-close visit with the 150 FourStroke while testing Premier pontoon boats in Minnesota. You’ll probably see lots of pontoons powered by this engine in the coming years, because its 1.92:1 gear ratio allows it to swing a larger-diameter prop for more thrust. Our test boat was the sporty 235 Solaris that has three 25-inch-diameter tubes. We got on plane in 3 seconds flat, and the torque-laden FourStroke took us to 25 mph in only 5.1 seconds with a top speed of 34.2 mph.
We also tested it on the Sun Tracker 24 with the XP3 triple-tube package that has lifting strakes on both sides on all three logs, which helped us get out of the hole even quicker, at 2.4 seconds. It was extremely quiet, registering only 55 decibels at idle. Our best cruise speed was at 4500 rpm, which netted us 27.2 mph and registered 83 decibels. We hit 25 mph in 6.5 seconds, and with it trimmed out we were sailing atop Table Rock Lake near Branson, Mo., at 37 mph.
While you’ll certainly be seeing Mercury 150 FourStrokes on pontoons, it’s a fair bet they will also be appearing on aluminum V-hull boats as well as on bay boats and even flats boats, thanks to the compact, light design.