Mercury MerCruiser
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Mercury MerCruiser 350 MAG ECT Mercury MerCruiser 350 MAG ECT
Mercury Marine’s MerCruiser 350 MAG is one of the most prolific engine platforms used to propel vessels under 35’ (10.7 m). Whether in single or twin-engine applications, this power plant has seen it all. The newest model incorporates Emission Control Technology (ECT) and is now ultra clean, meeting all Tier 3 EPA emissions requirements with its dual catalytic converters, wide-band oxygen sensors and refined engine control mapping. This modern adaptation leverages decades of hard-core development with advanced electronic technology to bring clean, quiet and efficient performance.

Mercury MerCruiser 350 MAG ECT Captain's Report

MerCruiser 350 MAG ECT

Twin applications are very popular with this engine platform, shown here is our test boat’s pair.


For our test, we chose to push the mighty small block with a heavy, twin engine sterndrive application. She measured 31’ (9.45 m) long with a beam of 9’6” (2.90 m) and weighed 11,220 lbs. (5,089 kg), which includes 97 gallons (367 L) of fuel on board. Our test vessel was also equipped with efficient Bravo 3 drives turning dual, counter-rotating stainless steel propellers.

On the test course, we achieved a top speed of 50.1 mph at 5200 rpm while consuming 48.1 gph. Best cruise speed was determined to be at 3500 rpm and resulted in an average speed of 31.6 mph to deliver 1.59 mpg.

MerCruiser 350 MAG ECT

The performance of our 31’ (9.45 m), 11,220-lb. (5,089 kg) test boat with twin MerCruiser 350 MAG ECT engines.

MerCruiser 350 MAG ECT

Calculated performance numbers from our test boat. Note the low sound readings at cruise speed (3500 rpm).

Block Talk

Based on a 5.7L, 350 V8 small block with sequential multi-port fuel injection (MPI), the mill breathes through a two-piece, long runner intake manifold with an 80 mm throttle body. The motor can spin up to 4600 to 5200 rpm, depending on the application. The 4’’ diameter bore and 3.48’’ stroke can easily burn 87 octane fuel with a compression ratio of 9.4:1, thanks to the ECU’s anti-knock programming that precisely controls ignition timing.

The cast iron block and heads are matted to iron exhaust manifolds with a dry joint design that prevents raw water from entering the cylinders.

Engine Management

MerCruiser’s ninth generation engine control unit (ECU) PCM 09 with SmartCraft CAN capabilities, onboard diagnostics (OBD-M) and dual oxygen sensors control the fuel delivery. In order to keep the fuel supply cool and prevent vapor lock, the engine features a special water-cooled fuel module that adds to the engine's reliability.

Fail-Safe Protection. The system is also equipped with Engine Guardian, a software that limits the engine from damaging itself should a low oil pressure or overheat situation occur. Also known as a ‘limp-home-mode’, the engine’s computer evaluates the problem and controls throttle position and fuel delivery, which effectively spares the engine from catastrophic damage.

Digital Option. A key selling point for the SmartCraft managed engines is the optional Digital Throttle and Shift (DTS). This allows fly-by-wire piloting and rigging with the added benefit of Axius joystick steering for twin-engine applications.

Corrosion Protection

MerCruiser’s cast-iron engine block and cylinder heads are coated with multiple baked-on layers of corrosion-fighting paint. The exhaust manifolds and elbows are sealed with an electro-deposition primer that is electrically fused to the metal.

Additionally, the transom assembly and drive unit are cast with Mercury’s exclusive XK 360 low-copper alloy treated with an irridite sealing process, along with statically applied EDP (Electro-Deposition Primer) that is followed by a final powder paint coating process for a tough corrosion-resistant barrier.

4-Way Protection. The engine is available in raw water, or closed loop cooling formats and features a brass seawater pump for longevity. Both configurations provide easy winterization with an air actuated, three point, water drain system for the raw water, while the closed cooling model is treated to long life (5-year) antifreeze. In order to reduce corrosion damage from being in the water, an active cathodic system called MerCathode is standard on all 350 MAGs with Bravo Drives or SeaCore Protection.


Making it Easy. Generally, inboard engines require little maintenance, and daily fluid checks are all that is required for that season. To improve upon this, MerCruiser identifies basic service items on the front of the engine with color-coded mapping for easy reference. Oil changes are simple with the remote, spin-on filter located on the front top of the starboard side of the engine. Engine accessories are all driven by a single serpentine belt that has an automatic tensioning feature.

MerCruiser 350 MAG ECT

MerCruiser engines feature a maintenance reference deal.

Drive Systems

Inboard engine configured boats can mate the 350 MAG to either the ZF 63A down angle transmission or the ZF 63IV for V-drive propelled vessels. Sterndrive boats can be rigged with any of MerCruiser’s drive options including the Alpha, and the Bravo Series in I, II, or III.

Corrosion Resistant. Boaters utilizing salt-water applications should take advantage of the hard coat aluminum anodized housings of the SeaCore treated drives that maximize longevity by minimizing corrosion potential. The SeaCore alloy is generally considered to be one of the best in the recreational marine industry. Customers choosing the DTS option can get the added benefit of electronic shifting while those with twin-engine rigging can enjoy the POD, like the maneuvering of Axius joystick steering when properly equipped.

MerCruiser 350 MAG ECT

The SeaCore drives are designed for the harsh saltwater environment.


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