Tech Stuff

Engine oil -- Conventional, synthetic or semi-synthetic blend? What's the correct engine oil for your customers' vehicles?

Pity the poor do-it-yourselfer who decides to purchase engine oil at an auto parts store or big-box retailer. There are products making all kinds of claims for all types of vehicles — heavy-duty pickups and SUVs; high-performance, high-revving engines; high-mileage older cars; and so on. What should you suggest? Of course, the owner’s manual is the place to start.

The standard new-car oil is usually a premium conventional (mineral) oil. Service level SM is the current designation and is available in a variety of viscosity grades. Most carmakers are now suggesting 5W-20 or 5W-30. Conventional motor oil works very well and with regular changes there is no reason that an engine won’t achieve 200,000 miles.

Many carmakers are now calling for full synthetic oil in their high-tech engines. Corvettes and most Mercedes-Benz vehicles come with it as a factory fill. Synthetic oils pass stringent tests and offer longer-lasting performance when it comes to viscosity index and protection against deposits. Synthetics flow better at cold temperatures and maintain excellent lubricity at high temperatures. They do not readily evaporate. However, along with being more expensive, not every engine needs them.

Synthetic blends offer protection for somewhat heavier loads and higher temperatures. They don’t evaporate as readily as conventional oils. They are a good choice for drivers who put heavy loads on the engine such as towing or off-roading. Semi-synthetics offer many of the same benefits of full synthetics, but at a fraction of the cost.

People are keeping their vehicles much longer, especially in this weak economy. As you know, it’s not uncommon to see odometers well into the six-figure realm in your service bay. Heat and time can cause seals, such as main bearing seals, to harden and crack. Oil blenders formulate products with seal conditioners that get into the pores of the seals, helping them stay flexible and maintain their shape. To compensate for engine wear, high-mileage oils may be near the upper range of a given viscosity designation — a thicker 30-weight than another bottle may be. They generally have more viscosity improvers and anti-wear additives, too.

GM dexos specification

As a sidenote, the General Motors powertrain engineers have developed the dexos™ (lower case “d”) engine oil specification. The result is engine oil designed specifically for GM engines. And just like GM, dexos is global. The dexos spec is designed to increase fuel efficiency, extend the life of the emissions system, require fewer oil changes, and produce fewer emissions.

The dexos oil also has some unique properties that General Motors engineers required. One characteristic is better resistance to aeration (the whipping of air bubbles into the oil). Some engines with variable camshaft timing also force the engine’s oil supply to serve double-duty as a hydraulic fluid. If the oil becomes aerated the hydraulic actuators won’t operate properly (similar to how silicone brake fluid can aerate in an anti-lock braking system). GM requires dexos oils to better resist aeration.

Like dexos, the new GF-5 specification developed by the International Lubricants Standardization and Approval Committee (ILSAC) with input from automakers, oil refiners, and oil additive manufacturers is expected to offer better performance. The new GF-5 and GM dexos are backwards compatible; they will work in engines that have used older previous formulations.

The goal is to extend the time and mileage between oil changes. Both dexos and GF-5 oils allow more miles between oil changes without a loss of lubrication qualities, sludge buildup, or damage to the catalytic converter. Depending on your customers’ driving habits, oil changes could extend beyond 10,000 miles.

What’s the correct engine oil for your customers’ vehicles?

You have seen the starburst symbol and American Petroleum Institute (API) donut on oil bottles so often, you may forget that they are there.

API’s Engine Oil Licensing and Certification System is a voluntary licensing and certification program that authorizes engine oil marketers who meet specified requirements to use the API Engine Oil Quality Marks. Some brands of oil do not have the API insignia and some marketers claim that they are smaller companies that can’t afford to submit each of their products for approval. We will not make any judgments here.

The API program is a cooperative effort between the oil industry and vehicle and engine manufacturers. Performance requirements, test methods, and limits are cooperatively established by vehicle and engine manufacturers, technical societies such as the Society of Automotive Engineers (SAE) and the American Society for Testing and Materials (ASTM) and industry associations like the American Chemistry Council and API. Oils meeting these requirements are recommended by vehicle manufacturers, says the API Web site.

Tags: engine oil 
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