28 Oct Start-Stop Technology Can Increase Bearing Wear

Nearly every technology shaping the auto industry can be traced to one goal: increased fuel economy. Engine start-stop technology is one more tool automakers have in their arsenals to ensure today’s vehicles meet tomorrow’s tightening fuel-economy regulations. Yet another reason to upgrade to AMSOIL synthetic motor oils.

In Principle, Start-Stop Technology Is Simple:

In automobiles, a start-stop system automatically shuts off the engine when your idling and restarts the engine when you take your foot off the brake, this allows the internal combustion engine to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. This is most advantageous for vehicles which spend significant amounts of time waiting at traffic lights or frequently come to a stop in traffic jams. Start-stop technology may become more common with more stringent government fuel economy and emissions regulations. This feature is present in hybrid electric vehicles, but has also appeared in vehicles which lack a hybrid electric power-train. For non-electric vehicles fuel economy gains from this technology are typically in the range of 3-10 percent, potentially as high as 12 percent. In the United States, idling wastes approximately 3.9 billion gallons of gasoline per year.

That’s not to say they’re without detractors, in fact, some automakers have installed off switches that allow motorists to disable the feature in response to negative driver feedback.

Consider These Statistics:

• According to bearing manufacturer MAHLE*, U.S. vehicles burned 3.9 billion gallons of gasoline while idling in 2017.
• Buick* reports that engines with start-stop technology increase fuel economy 4-5 percent using the EPA test cycle.

Automakers leap for joy over minuscule fuel-economy gains, they will continue  to stick with anything that may provide a 4-5 percent boost.

What Does That Have To Do With Motor Oil?

Most engine wear (friction) occurs during cold starts and also wear during warm starts.

Let’s get technical to understand why.

The crankshaft spins thousands of times per minute in a running engine. As it spins, oil flows through tiny openings in the crankshaft journals and fills the spaces between the journals and main bearings. The crankshaft literally floats on an oil film and doesn’t contact the bearings, which is called hydrodynamic lubrication. Which means, the bearings suffer little wear and last a long time.

Stopping the engine, however, reduces oil film thickness. The crankshaft settles onto the bearing surfaces rather than floats over them. The oil film thickness shrinks to about the same thickness as the surface roughness of the crankshaft. This is called boundary lubrication. Starting the engine allows the microscopic peaks on the metal surfaces to contact and cause wear until the oil film has been reestablished and the crankshaft is once again floating over the bearings. This is where the oil’s additives play a huge role in protection.

Granted, only minimal wear may occur each time the engine is started. It’s not a big concern in a properly maintained traditional engine using a good oil. But what if you greatly increase engine start-stop cycles?

Consider another statistic from MAHLE:

•  In equipped engines, start-stop cycles may triple over the engine’s lifetime compared to traditional engines.

That means three times more engine starts, three times more instances of boundary lubrication and three                 times more exposure to increased bearing wear.

Bearing wear can also snowball out of control. Metal particles can break off and populate the oil. The bearing surface becomes rougher, encouraging adhesive wear in which peaks on metal surfaces grab and tear the mating surfaces. Eventually the crank journal and bearing can weld together, ruining the bearing.

This all points to a simple directive: make sure customers with engines using start-stop technology are using AMSOIL synthetic motor oil to guard against bearing wear. Oil film thickness shrinks when engines start from a dead stop, placing even more importance on oil additives to maintain protection. Since engines equipped with start-stop technology spend so much more time under boundary lubrication, it’s vital to use  oil with superior film strength and additive quality. AMSOIL Signature Series Synthetic Motor Oil delivers. It provides 75% more engine protection against horsepower loss and wear to help protect today’s advanced engines.