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.

Fork Oil – Which do I use?

We sell a good amount of fork oil in Sioux Falls thanks to some great motorcycle shops who know how to maintain the various units out there. But if you have a shop manual, the right tools and some patience give it a try! Some units are very simple, quick and easy.

John Baker | Aug 22, 2019 10:33 AM

A fork oil’s number-one task is to deliver consistency. Consistent dampening despite temperature changes. Consistent rebounds despite different terrain. Consistent performance so you can ride or drive confidently.

Consistency.

What fluid would provide the best shock consistency?

Water.

Yes, water. But you don’t want to use it in your shocks for reasons you can probably guess, but we’ll get to that in a bit.

What shocks do

The shocks on your dirt bike, race car, ATV or other vehicle absorb abnormalities in the terrain and help stabilize the ride. They also absorb impact when landing a jump, taking some of the beating off the vehicle and your body. And they “load up” with energy when approaching a jump, helping you fly over whatever’s in your way.

The shock uses fluid to control dampening and rebound.

Say you’re riding your dirt bike and land a jump. The force depresses a piston inside the shock that pushes fork oil through calibrated valves. The fluid’s rate of flow through the valves influences the amount of dampening and rebound.

A thin fluid flows faster and results in quicker, springier shock feel. In contrast, a thick fluid flows more slowly and results in slower rebound and stiffer shock feel.

Fork oil viscosity matters

The fluid’s viscosity (often thought of as its thickness) influences how fast or slow the oil flows through the shock valves. If you prefer quick rebounds, use a lighter fluid. If you like slower rebounds, use a heavier fluid.

Buy AMSOIL Shock Oil

Easy, right?

Sure, if the viscosity of the shock oil never changes.

However, cold ambient temperatures increase the oil’s viscosity, resulting in slower rebounds. Then, after you’ve made a few laps and the vehicle’s heated up, the fork oil thins as it warms. That’s because fluids become thinner when they warm up. Think of molasses or honey. The warmer oil flows faster through the shock valves, leading to inconsistent shock feel.

H2O, no

That’s why water theoretically would provide the most consistent shock feel. Its viscosity doesn’t change between 33ºF (0ºC) and 211ºF (100ºC).

On a cold morning, after a long ride or on a blazing-hot day, water maintains the same viscosity provided it doesn’t freeze or boil. When was the last time you had a thin or thick glass of water? Hence, it would flow at the same rate through the shock valves, resulting in consistent feel.

Much more than flow, though

But the fork oil must do more than influence rebound and ride feel. It also must protect against wear and corrosion, two tasks at which water is notoriously bad.

The shock oil has to protect the shock tubes, seals and valves from wear as they constantly rub together. Minus good wear protection, the shock would tear itself apart in short order. Plus, the oil must form a layer on parts to prevent formation of corrosion. If corrosion starts, it won’t stop, spreading and depositing flakes of contaminant in the oil that act like sandpaper and scour metal parts until they’re worn out.

Look for a high-VI fork oil

Instead, look for a fork oil with a high viscosity index (VI). A higher VI indicates better resistance to viscosity changes throughout broad temperature swings. That translates into consistent shock performance and feel despite the ambient and operating conditions. And a consistent ride equals a more effective rider.

Points to consider when looking for fork oil

1) No standard viscosity

Your engine manufacturer recommends a specific viscosity of motor oil for best protection and performance. In the world of shocks, there are no universal viscosity requirements or recommendations. Each shock oil manufacturer is free to formulate its oils to whatever viscosity it deems appropriate. That means one brand’s “light” fluid could behave like another brand’s “medium” fluid, and so on.

2) Once you find a shock oil you like, stick with it

For the reasons listed above, avoid switching between fluids if you can. Once you have the proper suspension set-up for your body weight and riding style, stick with it. The shock oil is one of the biggest variables in your suspension tune, and messing with it can throw off suspension feel and your riding confidence.

3) Look at viscosity at 40ºC

If you decide to switch shock oil, compare the viscosity of the fluid you’re currently using at 40ºC to the same data for the new fluid. The closer the results, the more similar the oils will perform. Reputable manufacturers publish product data bulletins for their shock oils and post them online. If you can’t find a data sheet for the oil you’re considering, think twice before using it.

Buy AMSOIL Shock Oil

Category: Maintenance