Skip to main content

Engine start-stop technology – Major Wear Issues

Written by Charleen

Engine start-stop technology can increase bearing wear

Use only the best quality oil in these engines as the crankshaft needs to float. Even the “so called synthetics” don’t dampen the metal to metal issues mentioned below nearly as well as AMSOIL and you can tell due to the reduction in vibration or more consistent oil pressure as you rack up miles.

Yet another reason to upgrade to AMSOIL synthetic motor oil.

Matt Erickson | DIRECTOR, TECHNICAL PRODUCT MANAGEMENT

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.

In principle, start-stop technology is simple: the engine automatically shuts off while you’re idling and restarts when you take your foot off the brake. This reduces fuel wasted while idling. Automakers introduced different startstop systems in the late ‘70s and early ‘80s; however, drivers found them awkward and unworthy of the higher vehicle price. Today’s start-stop systems are less obtrusive and are available on vehicle models from most automakers.

Should be called Metal to Metal Contact Engine

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. But, despite their pitfalls, they’re likely not going anywhere. 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, so you can bet they’re going to stick with anything that may provide a 4-5 percent boost.

So, what does that have to do with motor oil?

Maybe you’re aware that most engine wear occurs during cold starts. Well, engine wear occurs during warm starts, too, like every time an engine equipped with start-stop technology restarts.

We have to 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. We call this scenario hydrodynamic lubrication. In this regime, the bearings suffer little wear and last a long time.

Run of the mill oils (95% on the shelf) are not going to provide protection with this condition

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 startstop cycles?

Consider another statistic from MAHLE:

  • Start-stop cycles in equipped engines 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 snowball out of control, too. 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 your 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 an 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.

This is especially needed in vehicles calling for 0W-20, 5W-20 and 0W-16.

Tech Articles, , , , , , , , , , ,

Low-viscosity doesn’t mean low quality

Written by Charleen

Low-viscosity doesn’t mean low quality

As motor oil viscosity continues to decrease, base oil and additive quality become more important.

Michael Meuli | VICE PRESIDENT, TECHNICAL DEVELOPMENT

Despite uncertainty surrounding future CAFÉ standards, fuel economy remains the biggest driver of innovation in the auto industry. One strategy for increasing fuel economy involves reducing energy lost to friction. Using lower-viscosity lubricants, which reduce pumping losses and flow easier at startup, helps automakers accomplish this goal. Just as we’ve become accustomed to 0W-20 oils, 0W-16 oil has entered the market and is recommended for the 2018 Toyota Camry and Honda Fit. People are wondering how much lower viscosity can go.

That’s because excessively low lubricant viscosity can reduce wear protection. Some people fear the fuel economy gains of modern low-viscosity oils aren’t worth the potential loss of wear protection. You should be familiar with the relationship between lubricant viscosity and wear protection, but it bears repeating.

Motor oil must develop a durable fluid film that separates engine components so they don’t rub together and wear out. As a rule of thumb, the higher the oil’s viscosity, the thicker the fluid film – and the better the wear protection.

That being the case, you might think it advantageous to throw out your 0W-20 motor oil and use 15W-50 instead. That’s a bad idea, and here’s why.

Modern engines are built with tighter clearances between parts than their predecessors. Let’s take the GM* 3.8L engines we test in our mechanical lab as an example. The clearances between the crankshaft journals and main bearings can be as low as .0007 inches. That’s thinner than a sheet of paper (about .004 inches).

During operation, oil continuously flows through tiny ports in the crankshaft journals to lubricate the journal/ bearing interfaces. It should form a strong, consistent oil film on which the crankshaft journals float as they spin, preventing them from touching the bearings. This is called hydrodynamic lubrication. Oil that’s too thick for the engine, however, may not flow fast enough to fill the clearances, allowing the high spots on metal surfaces to contact. This is called boundary lubrication.

In this case, using a higher viscosity oil than what’s recommended in your modern engine would lead to increased wear. Adding insult to injury, it would reduce fuel economy and increase operating temperatures as well.

Viscosity that’s too low, however, can have the opposite effect. Since viscosity is related to film thickness, low-viscosity oil may not develop an adequate fluid film to keep metal components separated, leading to wear. If bad enough, parts will eventually weld together and destroy the engine.

You can see how modern engines have put oil formulators into a bind. How do we formulate low-viscosity oils that maximize fuel economy while also providing good wear protection in today’s stressful engines?

In a word, quality.

Although oil film thickness is related to lubricant viscosity, film strength is a function of base oil and additive quality. We start with high-quality synthetic base oils that offer naturally high resistance to heat and chemical breakdown.

The challenge, however, is that lower viscosity oils tend to be more volatile, meaning they burn off more easily when exposed to high heat. If you ever look at a motor oil’s NOACK Volatility, you’ll notice volatility tends to increase as the oil viscosity decreases. This is of particular importance since most new vehicles are equipped with turbocharged engines, which generate increased heat. High volatility can lead to excessive oil consumption, which causes the oil to thicken, making it harder to pump through the engine and reducing fuel economy. Oil that has thickened can also lead to deposits and disrupt the additive balance.

That’s why only synthetic base oils can be used to formulate a 0W-16 motor oil. Conventional base oils are too volatile to meet requirements of low-viscosity oil.

Additives, too, play a vital role in low viscosity oils. We talked about boundary lubrication earlier. When in a boundary lubrication situation, protecting against metal-to-metal contact falls on the motor oil’s anti-wear additives, more so than with higher viscosity oils. The additives form a sacrificial barrier on metal parts that absorbs contact and protects the metal surfaces.

Motor oil quality has always been important, but modern low-viscosity oils underscore the point. That’s good news for Dealers selling the best oil on the market.

To help you reach this market, we introduced new OE 0W-16 Synthetic Motor Oil (OES) last month. We’ll monitor demand for 0W-16 oils and introduce additional formulations if demand dictates.

In the meantime, brace yourself for 0W-8 motor oil, which is already being tested in Japan.

Maintenance, , , , , , , , , , , , , ,