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Motor Oil: How To Choose The ‘Right’ Oil

To keep up with the lubrication requirements of all the different vehicle manufacturers, oil companies have had to expand their product lines to include new ultra-low, multi-viscosity, fuel-saving oils as well as products with special additive packages for specific engine applications.

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In recent years, the variety of different motor oils that are now available to consumers has multiplied exponentially. To keep up with the lubrication requirements of all the different vehicle manufacturers, oil companies have had to expand their product lines to include new ultra-low, multi-viscosity, fuel-saving oils as well as products with special additive packages for specific engine applications.

Consequently, it’s more important than ever before to make sure your customers buy the correct motor oil for their vehicles. Why? Because using the wrong oil may cause problems as well as void the OEM powertrain warranty. Many late-model vehicles with extended oil drain intervals (those that recommend oil changes of 7,500 miles or higher) and high output turbocharged engines often require a full synthetic motor oil with an additive package that meets specific OEM performance requirements.

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This includes GM’s “dexos” requirements for their 2011 and newer vehicles — especially those with oil life monitors that turn on a service reminder light when the system estimates the oil needs to be changed. Synthetic oils are usually superior to conventional oils or synthetic blends in terms of high and low temperature performance as well as durability. But if the additive package isn’t right for the application, it’s not the right oil to use.

European auto makers are very picky about the type of oil that goes into their engines. Oils that meet current American Petroleum Institute (API) “SN” standards or ILSAC GF-5 standards for Asian vehicles may not always meet the specifications required for European applications. Specially formulated “Euro” oils typically have higher temperature and durability requirements than many of their domestic counterparts.

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Oil specifications can also vary from one European automaker to another, and by the year, make, model and engine in the vehicle. That’s why buying motor oil off the shelf takes a little more homework these days. Choosing the right oil involves checking the vehicle owners manual to find out what type of oil is required.

This includes not only a recommended viscosity rating but also a performance specification. Oil requirements also may be marked on the engine oil filler cap or dipstick. Many late-model engines are factory filled with multi-viscosity 0W-20, 5W-20 or 5W-30 motor oil, while some European cars may specify a 0W-40.

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With diesel applications, most pickup trucks still call for a traditional 15W-40 but some are now specifying 5W-40. For European diesel passenger car engines, 5W-40 is commonly specified. What about older gasoline-powered cars and trucks? Good ‘ol 10W-30 or 10W-40 are still good choices for these applications, with 20W-50 being a good hot weather upgrade for hard-working trucks. For high-mileage vehicles with more than 75,000 miles on the odometer, you can always recommend a “high-mileage” motor oil that contains extra viscosity improvers and additional seal conditioners that help rejuvenate aging seals to prevent oil leaks.

Most engines from the 1990s forward have roller lifters or overhead cams. But many older engines (1980s and older) have flat tappet cam pushrod engines that require a higher dose of anti-wear additive than today’s engines. In 2005, “SM” rated motor oils were introduced that drastically reduced the amount of ZDDP (Zinc Dialkyl Dithio Phosphate) anti-wear additive. Further reductions of ZDDP were made again when the current “SN” and GF-5” motor oils were introduced. ZDDP is an anti-wear extreme-pressure additive that protects cam lobes and lifters.

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The problem is that the phosphorus and zinc in ZDDP can shorten the life of the catalytic converter. So for an older flat tappet pushrod engine, you should recommend a motor oil that is fortified with extra ZDDP anti-wear additive.

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