Skip to main content

Why Does Motor Oil Turn Black?

Why Does Motor Oil Turn Black?

Motor Oil Turning Black Isn’t an Indicator of Bad Oil

What causes black motor oil? And when your oil darkens does it mean it’s time to change it? Well, there are a couple of factors that can cause the former. Let’s dig in.

Factors causing black motor oil

Heat cycles naturally darken motor oil

During your drive to work in the morning, your engine reaches normal operating temperature (typically 195ºF-220ºF), heating the motor oil. Then the oil cools while your car sits in the parking lot. During lunch, the oil again is exposed to heat during your drive to Walmart for butter and shoe laces. The process repeats on the way home. And the next day. And the next.

That’s what’s meant by “heat cycles.” The continual exposure to periods of high heat naturally darkens motor oil.

Some additives in motor oil are more susceptible to darkening in the presence of heat than others. In addition, normal oxidation can darken oil, too. Oxidation occurs when oxygen molecules interact with oil molecules and cause chemical breakdown, just like how oxygen causes a cut apple to brown or iron to rust. High heat accelerates oxidation.

Soot causes oil to turn black

While heat cycles cause oil to darken, soot causes oil to turn black. Most people associate soot with diesel engines, but gasoline engines can produce soot as well, particularly modern gasoline-direct-injection engines.

Soot is a byproduct of incomplete combustion. Since soot particles are less than one micron in size, they typically don’t cause engine wear. For comparison, a human hair is roughly 70 microns in diameter.


If soot particles agglomerate into larger wear-causing contaminants, the oil filter will catch them. Sometimes people who use bypass filtration systems, which can filter contaminants down to two microns, express surprise that the motor oil is still black. Soot, however, can still elude filtration down to two microns. Any finer filtration and the filter could catch dissolved additives in the motor oil.

Oil Myth: The color of the oil indicates when it’s time for an oil change

It’s common to assume that black motor oil has worn out or become too saturated with contaminants to protect your engine and requires changing. Not necessarily. As we saw, discoloration is a natural byproduct of heat and soot particles, which are too small to wear out your engine.

The only surefire way to determine if the oil has reached the end of its service life is to perform oil analysis. Chemically analyzing an oil sample reveals the condition of the oil, the presence of contaminants, fuel dilution and so on. Several companies offer oil analysis services, including Oil Analyzers INCWe keep the kits here in Sioux Falls

Absent oil analysis, it’s best to follow the oil-change recommendation given in your vehicle owner’s manual or by the motor oil manufacturer. The recommended service intervals for AMSOIL products, for example, are based on thousands of data points spanning years of use.

It’s best to trust the data, not your eye, in this case. Otherwise, changing the oil could amount to throwing away good oil.

Time for an oil change? Find AMSOIL product for your vehicle here.

Soot isn’t just for diesels anymore

Amsoil Tech Guru

Soot isn’t just for diesels anymore

Today’s gas engines can produce as much soot as yesterday’s diesels.

Matt Erickson | TECHNICAL MANAGER – PCLT PRODUCTS AND MECHANICAL R&D

I bet most of you reading this have some level of emotional attachment to traditional vehicles. The muscle-car era of the 1960s and 1970s kindled a lifelong passion for cars in millions of Americans and Canadians. And how many of you who grew up in the 1980s had a supercar poster or two on your bedroom wall? Today, based on sales, big pickup trucks seem to be everyone’s favorite vehicle.

With fuel-economy regulations slowly reshaping the industry, it’ll take more than nostalgia to maintain the viability of the internal combustion engine. They must continue to become even more efficient and clean-running.

That’s one reason for the proliferation of turbocharged gasoline-direct-injection (T-GDI) engines over the past several years. Directly injecting fuel into the combustion chamber as opposed to an intake port upstream of the cylinder, as with a port-fuel-injected engine, offers more precise control over fuel delivery. This arrangement increases fuel economy and reduces CO2. T-GDI engines are also smaller and lighter than traditional engines that make similar power, helping automakers reduce weight and boost efficiency.

It’d be great if the story ended there. We’d all drive into the sunset in our pickups that deliver the perfect combination of comfort, functionality and efficiency. But somewhere along the way engineers noticed a strange phenomenon: Some T-GDI engines were experiencing abnormally high rates of timing chain wear, and many think soot is at least partially to blame.

You’re probably thinking, “But diesels produce soot, not gasoline engines.” Wrong – at least with T-GDI engines. When engineers borrowed the practice of directly injecting fuel into the combustion chambers of diesel engines and applied it to their gasoline counterparts, soot production tagged along. In fact, on some light-colored T-GDI vehicles, you can see a ring of soot on the bumper near the exhaust.

Soot, which is made of carbon, is the result of incomplete combustion. In a port-fuel-injection engine, gas and air mix in the intake port prior to entering the combustion chamber. This arrangement allows ample time for the gas and air to mix more completely, which results in more complete combustion. In direct-injection engines, the gas doesn’t have as much time to mix with the air since it’s injected directly into the combustion chamber. Plus, it’s injected later during the operating cycle, further reducing its ability to completely mix with the air. As a result, direct-injection engines can result in less-complete combustion – and increased soot. Believe it or not, some modern T-GDI engines produce more soot than older diesels not equipped with particulate filters. That’s one reason gasoline particulate filters are in development now and could soon end up on your next T-GDI vehicle.

All that soot is bad news for the timing chain. The particles can agglomerate into larger particles that wear out timing-system components and other sensitive engine parts prior to lodging in the oil filter. If bad enough, the chain can elongate and jump the teeth on the sprocket, throwing off timing enough to kill the engine. The chain could also break, which can result in catastrophic and expensive damage if, for example, a piston strikes and breaks a valve.

Fuel dilution may also be to blame for timing chain wear since excess fuel in the oil causes the oil to lose viscosity, which reduces wear protection. Though experts are still studying the problem, they have soot in their sights and are working hard to develop a test that measures an oil’s ability to protect against soot-related wear. The current test under development uses a Ford* 2.0L Ecoboost* engine to evaluate timing chain protection. The final details of the test are still being ironed out, but it’s well on its way and slated for inclusion in the forthcoming GF-6 motor oil specification, set for introduction in 2019.

We’ve already run the test, and I’m happy to say that Signature Series Synthetic Motor Oil performed extremely well. Oil formulation, specifically additive systems, plays a huge role in how the oil handles soot. The oil needs the correct dispersant and detergent additives in the correct concentrations to hold soot particles in suspension and prevent them from agglomerating into larger, wear-causing particles. Our oils are formulated with potent additives that keep soot in suspension to protect your engine.

Good filtration is just as important in today’s engines. Our Ea® Oil Filters’ synthetic media offers improved efficiency and capacity, helping ensure agglomerated soot is safely trapped in the filter and doesn’t ruin your engine.

As engines grow more complicated, so do the challenges they present. That’s why we remain diligent about identifying problems to engine life and developing solutions. That way we can all drive off into the sunset in the vehicles we love without worrying about wear.

Solve ethanol issues before they arise

Ethanol Issues

Prevent Ethanol Issues Now

The fuel some love to hate isn’t the problem – letting gasoline sit too long is the real problem.

Len Groom | TECHNICAL PRODUCT MANAGER

How did an alternative fuel made mostly from corn grown in the Midwest become a political lightning rod?

Whatever the reason, ethanol is always a controversial topic. Some love it, citing its ability to reduce our dependence on foreign oil while supporting American jobs. Some hate it, saying it reduces fuel economy and wastes farmland that could be used to grow food.

I’ll leave that debate to someone else. Instead, I want to talk about the effect ethanol can have on fuel-system components, especially in powersports and lawn & garden equipment – and what you can do to avoid those problems.

What is ethanol?

But first, some background info. Ethanol is an alcohol fuel derived from plant materials, such as corn, barley or wheat. It’s mixed with gasoline at different ratios to produce the fuel you buy at the pump. Most of us are familiar with E10, which is gasoline that contains up to 10 percent ethanol. Today, E15 is becoming more common. And owners of flex-fuel vehicles designed to run on increased concentrations of ethanol can opt for E85.

The upside of ethanol

Years ago, lead was added to gasoline to, among other things, boost octane rating and help prevent engine knock. It turned out lead poisoned catalytic converters and harmed the environment, so it was replaced by methyl tert-butyl ether (MTBE). However, MTBE was shown to damage the environment if leaked or spilled. Today, ethanol has replaced MTBE as a more environmentally friendly means of boosting octane.

Fuel-system problems

That brings us to a major knock on ethanol – it’s propensity to degrade rubber and plastic fuel hoses and carburetor components. Ethanol can cause gaskets and fuel lines to harden, crack and then leak. It can also cause aluminum and brass fuel-system components to corrode and develop a white, flaky residue that clogs fuel passages. Some marina personnel I’ve talked to say up to 65 percent of their repair orders are attributed to fuel-system problems.

PHASE SEPARATION

Ethanol isn’t to blame

While ethanol has become a popular scapegoat for mechanics, especially in the marine industry, it isn’t the enemy – time is the enemy. Why do ethanolrelated problems affect powersports and lawn & garden equipment more than your car or truck? Because your boat or lawnmower can sit idle for weeks or even months. During that time, the fuel can absorb moisture since ethanol has an affinity for water. That’s why ethanolrelated problems are so common in marine applications. Water can break the molecular bond between gasoline and ethanol, causing the water/ethanol mixture to separate from the gasoline and fall to the bottom of the tank. This is known as phase separation, and you can see an example of it in the image above.

Phase separation causes a couple problems. The engine can draw the ethanol/ water mixture into the carburetor or injectors, leading to a lean-burn situation that can increase heat and damage the engine. In addition, the gasoline left behind no longer offers adequate resistance to engine knock since the ethanol that provides the increased octane the engine needs has separated from the gasoline. Burning low-octane gas can cause damage due to engine knock, especially in two-stroke engines. Finally, if your boat, lawnmower or other piece of equipment sits unused, the water/ethanol mixture can slowly corrode aluminum and brass fuel-system components, not to mention rubber and plastic fuel lines and gaskets. Eventually those components fail and require replacement.

Driving your car or truck almost every day doesn’t allow enough time for phase separation to occur, which is why we don’t see these issues nearly as often in the passenger car/light-truck market.

Prevention is the best solution

Although some fuel additives on the market claim to reverse the effects of phase separation, there’s no way to reintegrate gasoline and ethanol once they’ve separated. Instead, it’s best to prevent it.

One solution is to use non-oxygenated, ethanol-free gas in your powersports and lawn & garden equipment. It costs a little more, but it eliminates problems associated with ethanol. Another solution is to treat every tank of fuel and container of gas with AMSOIL Quickshot®. It helps keep water molecules dispersed in the fuel to prevent phase separation. It also cleans varnish, gums and insoluble debris while stabilizing fuel during short-term storage.

It’s a great way to avoid ethanol-related problems and keep your equipment protected. There’s nothing controversial about that.

How do we define “severe service”?

Buick 3.8 Engine Oil Testing

How do we define “severe service”?

When pushing our lubricants to their limits, we sometimes find the limits of the test equipment first.

Matt Erickson | TECHNICAL MANAGER – PCLT PRODUCTS AND MECHANICAL R&D

One of my responsibilities here at AMSOIL is to help develop tests in our mechanical lab designed to push lubricants to their limits, both ours and those of our competitors. An effective performance test accelerates lubricant degradation and forces the oil to its breaking point sooner than if tested in the field. This provides more data, faster.

The definition of “severe”

Given the severity of our testing, what happens when the equipment we test fails before our lubricants? Honestly, it causes us to simultaneously rejoice and curse. On one hand, we know our products withstand the toughest conditions we throw at them. On the other, we have to contend with the extra cost and hassle of test equipment that just isn’t built to handle the punishing conditions.

The August 2016 Tech Talk revealed how some two- and four-stroke equipment we’ve tested couldn’t stand up to our test conditions. We’ve run into the same predicament in the passenger car/light-truck market, too.

One recent incident involved the popular General Motors* 3.8L motor. Historically, the GM 3.8L is a rocksolid engine that’s powered millions of cars over the years. It’s a fixture in industry performance testing. One standardized test uses this engine under severe conditions for 100 hours. But our oils soldier through that test like a walk in the park, so we have to triple its length to 300 hours to get useful data. Not an easy task for equipment not designed to handle such extremes.

Well, we recently blew up a GM 3.8L engine. The image shows some of the carnage we found after removing the oil pan. All those bits and pieces used to be a piston.

We ran this test under extreme conditions, as if you were towing continuously at highway speeds uphill for weeks.

Unleaded gasoline

What happened, you ask? First, I’ll ease any concerns you might have: it wasn’t the oil’s fault. We were in uncharted territory, never having an oil last so long in this test before, so we knew we were on borrowed time. In fact, after more than four weeks of testing, the oil hadn’t even reached its breaking point. One of the exhaust valves broke off and fell into the cylinder, where it and the piston were pulverized into the mess you see here. As the piston and valve debris made its way to the oil pan, the crankshaft caught it and blew a hole in the side of the engine block. The severity of our test conditions combined with valve seat recession are to blame.

Years ago, lead was added to gasoline to, among other functions, lubricate the valve seats. Once lead was officially banned from gasoline, in 1996, the fuel no longer provided the same level of valve-seat protection. This lack of protection, combined with the extreme conditions of our test, invited valve recession. When valve seats recede, the valve no longer seats evenly. The result is a loss of heat-transfer that overheats and erodes the valve, as well as an uneven side load that causes the valve to bend slightly on every cycle. This onetwo punch eventually caused the valve to fail. We ran this test under extreme conditions, as if you were towing continuously at highway speeds uphill for weeks. Oil temperatures exceeded 300ºF. The extreme, 1,500ºF exhaust gas temperatures, combined with the constant stress of unevenly eroded valve seats, eventually led to valve failure, snapping a valve in half and destroying the engine.

But our oils soldier through that test like a walk in the park, so we have to triple its length to 300 hours to get useful data. Not an easy task for equipment not designed to handle such extremes.

Suitable for continued use

The good news, however, is the motor oil was still good. Even after hundreds of hours of operation so severe it destroyed the engine, the oil analysis still looked great. It made me smile to see our oil last that long, but it also made me cringe because we were going to have to once again re-test to try to get the oil to break.

This conundrum might present challenges to us engineers, but it amounts to you and your customers receiving the best synthetic lubricants available. We’re happy to keep blowing up engines in our mechanical lab to ensure your engines are protected out in the field.

Given the severe nature of our performance tests, the test equipment sometimes fails before our lubricants.

Can Your Motor Oil Handle the Seven Responsibilities of a Lubricant?

Spring Oil Change

Can Your Motor Oil Handle the Seven Responsibilities of a Lubricant?

Most motorists understand the primary functions of motor oil: reduce friction and wear. However, motor oil and other lubricants must do more to protect your vehicles and equipment. With engines and equipment becoming more powerful and sophisticated, it takes a properly formulated, well-balanced lubricant to carry out these seven critical functions.


• Minimize Friction

Lubricants reduce contact between components, minimizing friction and wear.

• Clean

Lubricants maintain internal cleanliness by suspending contaminants within the fluid or by preventing the contaminants from adhering to components. Base oils possess a varying degree of solvency that assists in maintaining internal cleanliness. Solvency is the ability of a fluid to dissolve a solid, liquid or gas. While the solvency of the oil is important, detergents and dispersants play a key role. Detergents are additives that prevent contaminants from adhering to components, especially hot components such as pistons or piston rings. Dispersants are additives that keep contaminants suspended in the fluid. Dispersants act as a solvent, helping the oil maintain cleanliness and prevent sludge formation.

• Cool

Reducing friction minimizes heat in moving parts, which lowers the overall operating temperature of the equipment. Lubricants also absorb heat from contact surface areas and transport it to a location to be safely dispersed, such as the oil sump. Heat-transfer ability tends to be a trait of the base oil’s thickness – lighter oils tend to transfer heat more readily.

• Seal

Lubricants act as a dynamic seal in locations like piston rings and cylinder contact areas to prevent contamination.

• Dampen Shock

A lubricant can cushion the blow of mechanical shock. A highly functional lubricant film can resist rupture and absorb and disperse these energy spikes over a broad contact area. As the mechanical shock to components is dampened, wear and damaging forces are minimized, extending the component’s overall operating life.

• Protect

A lubricant must have the ability to prevent or minimize internal component corrosion. Lubricants accomplish this either by chemically neutralizing corrosive products or by forming a barrier between the components and the corrosive material.

• Transfer Energy

Because lubricants are incompressible, they can act as an energy-transfer medium, such as in hydraulic equipment or valve lifters in an automotive engine.

Lubricants do far more than simply protect against wear. High-quality lubricants – like AMSOIL synthetic lubricants – are formulated to excel in each of these critical areas, ensuring you get the most out of your vehicles and equipment.