Step Up Intervals

What is the best service interval for this most basic of maintenance?

underhood oil changes oil change intervals motor oil changing oil automotive aftermarket technicians

The 3,000-mile oil and filter change; it's as much a part of the American car culture as hot rods, car hops and white wall tires. Most of us can count this maintenance as our first automotive service experience. Whether we performed it ourselves in the driveway or watched as the family "mechanic" put the car up on the lift and drained the oil, the 3,000-mile number has been ingrained into our culture as the standard interval for oil change service.

A quick look through the owner's manual of most any vehicle built since 1970 will reveal that while the 3,000-mile interval has been the most heavily recommended in the past, manufacturers regularly have been recommending longer intervals. As consumers began to look for lower maintenance vehicles, parts of the industry began to openly challenge the 3,000-mile convention. In particular, European manufacturers, supported by the European Automobile Manufacturers Association, have long sought the ability to reduce oil use, whether it was by increasing fuel economy or reducing the frequency of oil changes. The domestic manufacturers were not far behind.

As a benefit to new 1975 Chevrolet owners, General Motors announced its new "Efficiency System." It included extended maintenance intervals stretched to between 6,000 and 7,500 miles for oil changes and spark plugs that lasted up to 22,500 miles compared to 10,000 miles on 1974 models. This increased emphasis on efficiency occurred as an effect of the 1973-74 oil embargo, which saw oil prices quadruple to $75 a barrel and gasoline rationing that used license plate numbers to determine when vehicle owners could purchase fuel.

Today, service intervals are being stretched further than ever. According to the Motor & Equipment Manufacturers Association (MEMA), the move toward extended service intervals appears to be three-fold. First, new oil technologies have allowed the manufacturers and refiners to create more stable oils that will endure longer service. Second, decreased frequency of traditional tune-up services such as spark plugs and transmission oil have led to less frequent visits for service. And finally, consumers have demanded that oil changes follow suit.

Engine Oil Evolution

Engine oils traditionally have been made from a petroleum hydrocarbon base oil stock derived from crude oil. They are defined by category with Group I being the least refined and Group III the most refined. Synthetic base oil stocks are produced by highly processing and refining Group I, II or III mineral based oils, or by chemically engineering base oil stock as in Group IV and V.

In the mid 1970s, synthetic oil base stocks were formulated and used for the first time in automotive applications. Higher purity with the ability to control oil properties better allowed synthetic oils to function well at extremes of engine temperature, while requiring little or no viscosity index improvers, the oil components most vulnerable to degradation as the oil ages.

By the early 1990s, many European manufacturers felt that the American Petroleum Institute (API) oil standards were not compatible with their own European-designed high performance engines. The American style of synthesizing oil concentrated on highly processing mineral base stocks, while the demands of European engines favored pure synthetics. As a result, many leading European motor manufacturers created and developed their own oil standards.

In February 2005, ExxonMobil was the first major oil company to mass market extended performance oils, the mineral based Mobil Clean 5000 and the synthetic blended Mobil Clean 7500. According to the company's literature, "Mobil Clean 5000 has an extra level of cleaning performance, 16 percent more cleaning additive than our conventional oil... " and "Mobil Clean 7500 is a synthetic blend formulation with a boosted level of cleaning performance, 27 percent more cleaning additives than Mobil Clean..." Both oils were designed to "keep your engine cleaner longer."

According to a special report released by MEMA, "extended drain technology is primarily based on the availability of synthetic oils. While the additives in conventional, non-synthetic oils allow them to function longer than the traditional 3,000 miles, it is primarily the synthetic base stocks that allow the oil to last much longer. Synthetic oil offers many advantages in durability versus conventional petroleum oil and it is all based on the synthetic oil's superior heat and oxidation resistance. Synthetic oil is more accurately controlled at the molecular level and therefore can be engineered to resist the forces in an engine that works against oil durability."

How Long Does Engine Oil Last?

Clearly there is a degree of ambiguity about how long motor oil actually lasts. Traditionally, vehicle owners have felt more comfortable with convenient mileage or time-based schedules while others prefer seasonal changes, but the question still remains — how long does engine oil last?

Many factors contribute to the degradation of motor oil. Extreme heat breaks down oil molecules, which evaporate and leave deposits on internal engine surfaces inhibiting the transfer of engine heat to the oil. Oxidation, which is accelerated by heat, further inhibits heat transfer. Environmental contaminants such as dust and dirt enter the engine through improperly maintained filters, and normal engine wear produces metallic particles that travel through the engine, increasing wear. Byproducts of normal combustion – soot, dirt, and sludge – contaminate the oil and change viscosity. Finally, internal pressure breaks down the oil film between moving parts, which agitates the oil, trapping and suspending air that promotes oxidation.

Lubricant manufacturers have continually researched and experimented with various chemical additives. In addition to viscosity index improvers, which are the primary additives that allow for multi-grade oils, rust and corrosion inhibitors are used to neutralize acidic oxidation of the oil. Detergents and dispersants used to minimize sludge buildup, along with anti-foaming agents and pressure additives, prevent the breakdown of the oil barrier between internal engine parts. This is known as the shear factor. A petroleum cocktail is then blended to each company's specification with different additives used depending on the application (diesel engine, gas engine). The API sets the minimum performance standards for all oils in the U.S.

While additives are designed to aid the base oil in the protection of engine components, each has its limitations and can be affected by the same factors that degrade base oils. With lubricant additive packages comprising approximately 20 percent of a typical multi-grade oil, the best answer to our question of how long engine oil lasts is, "it all depends."

Extended Drain Intervals

Current demand on the lubricant industry from both the government and consumer groups to meet longer drain intervals continues to increase. Fueled by both monetary and environmental concerns, the automakers have adopted 100,000-mile tune-up and coolant change intervals, which make the 3,000-mile oil service interval seem unreasonable.

Environmental advocates charge that used oil that is not properly recycled often finds its way into waterways via storm water systems. They also note that just one gallon of used oil can foul the taste of 1 million gallons of water and that extending the life of 4 to 5 quarts of engine oil can potentially reduce carbon dioxide (CO2) emissions by more than six grams per mile through a reduction in processing and transportation emissions.

Responding to these concerns, ExxonMobil, in introducing its extended performance oils, states, "Mobil's Extended Performance oils are marketed based on the fact that consumers are currently going longer between oil changes. However, if less used oil is discarded through the introduction of these products, this would represent a positive impact on the environment."

Oil Life Monitoring Systems

One solution presented by the automobile manufacturers is the oil life monitor. First introduced by BMW, the system was featured on the 1982 528e. Oil life monitors allow the manufacturer the ability to extend maintenance intervals without relying on the owner to determine anything involving oil service life. According to MEMA, "this reduces the involvement of the car operator in determining service intervals, which is a priority of many manufacturers."

Several types of systems exist that use technology to directly "read" the oil. The most popular of these systems relies on capacitance or conductivity. There are only subtle differences between the technologies.

Capacitance-based systems measure the amount of electric charge stored (released) for a given amount of electricity supplied. Using two conducting plates separated by the oil, which acts as an insulating fluid, a base capacitance number is calculated. As the oil degrades, the change in capacitance is measured.

Conductivity-based systems also rely on the oil as an insulator. All materials have a dielectric constant. This is a number that defines the ability of a material to carry alternating current and compares it to the same material under the perfect conditions of a total vacuum. By measuring this ratio, the system is able to detect when a change has occurred in the oil that alters the oil's insulating, or dielectric, properties.

Other systems are based on algorithms that attempt to predict oil change intervals. Based primarily on research which showed that oil breakdown is determined by such factors as driving habits, driving speed and failure to replenish low oil levels, algorithm method systems monitor time between oil changes, vehicle speed, coolant temperature, load signal, engine rpm, engine oil temperature and engine oil level to determine the remaining time and mileage before the next oil change. General Motors' Oil-Life™ System and Chrysler Corporation's Flexible Service System (FSS) are good examples of this type of system.

Most recently, Bosch developed a multifunctional system that will determine oil level and oil condition. A piezoelectric listening device determines the viscosity. When this sensitive surface comes into contact with the oil, the oscillation frequency and damping are changed according to the oil's mechanical properties, allowing viscosity to be determined. The addition of oil level sensing capability may allow the oil dipstick to be eliminated from the engine.

With the latest oil life monitors utilizing connectivity programs, like BMW's Assist and GM's OnStar, which enable a vehicle to notify the dealer itself when an oil change is required, maybe the next big advancement in oil change technology will be the maintenance-free vehicle.