Marine Engine Oiling

Keep marine engines well oiled at extreme angles.

October 13, 2014

At age 14, I got a minibike with a 3 hp Briggs & Stratton engine, and one day I decided to lay it over to clean the mud from underneath. Big mistake. By the time I came back with cleaning materials, motor oil was pouring out of the engine and had drenched the combustion chamber, manifold and carburetor, not to mention our family patio.

That taught me to keep four-stroke engines upright. Yet, how does that apply to marine engines that are subjected to pitch and roll, sometimes in the extreme, like the U.S. Coast Guard’s 47-foot MLB (Motor Lifeboat) that can roll over, right itself and keep running?

Spin Move
A new class of rollover rescue boat, the Nh1816 built by Royal Netherlands Sea Rescue Institution in Holland, is powered by a pair of MTU Series 2000 M94 V-8s driving Hamilton water jets via ZF 2000 transmissions.


The 63-footer rights itself within 30 seconds if overturned. Yet supplying lubrication to the engine during one of these episodes poses a big challenge.

Each 1,200 hp MTU features a deep oil pan with an oil pickup circuit to maintain adequate pressure at extreme angles — even upside down, says Gary Mason, senior public relations manager for Michigan-based MTU America. “In addition, baffling in the oil pan minimizes sloshing in rough sea conditions,” he reveals.

Gravity Falls
To keep oil from spewing out, MTU integrated a valve in the crankcase breather that closes when the vessel heels over but opens when the vessel returns to a less severe angle.


To guard against too much pressure, there’s a second breather on the lower portion of the gear case housing.

A solenoid valve in the breather system prevents oil from entering the cylinders during a rollover. Since a diesel engine can run on its own motor oil, this prevents uncontrolled combustion.

During a rollover, a switch disengages the drive and reduces rpm to idle to prevent over-revving and minimize stress on the drivetrain. Once the boat rights itself, the captain can re-engage the gears and throttle up.


Your Engine
What kind of angles can your engine endure? Mercury Marine designs its inboards for a maximum sustained angle of 20 degrees, says Daniel Clarkson, Mercury’s director of product integration.

“If you’re in the boat, that much angle feels pretty uncomfortable,” Clarkson says.

Yet, Mercury is working to increase maximum angles for wakeboarding enthusiasts, who shift weight to one side, forcing the boat to heel over on its gunwale and create a unique wake shape. “It’s about as extreme a static angle as you will find on a recreational boat,” Clarkson says.


Mercury uses a deep-sump oil pan with baffling to control oil sloshing. The oil pickup is also placed as deep as possible in the oil pan.

Clarkson also works with Mercury boat-partner companies to design fuel tanks with sumps and pickups set deep to avoid starving the engine of fuel at extreme angles.


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