Car-care experts, mechanics, and automakers alike have called motor oil the lifeblood of your engine, and it's easy to understand why. Motor oil is the lubricant between highly loaded moving parts; but it also helps engines keep their cool and helps maintain tight manufacturing tolerances.
Altogether, the oil that you choose can have a significant influence on how long your engine lasts, how well it perfoms, and how smoothly it runs, as well as whether its gas mileage is as good as it should be.
Here are six pieces of useful and potentially money-saving advice regarding choosing the best oil:
Go with what's recommended. Our first piece of advice is that your car's engine was designed to run on a particular type of oil. Those engineers knew when they chose the particular oil that's recommended for your model, that it would provide the ideal performance for most conditions. So check in your owner's manual and note the viscosity (5W-30, or 20W-50, for instance) and the API service rating (SJ, SL, or SM, for example). If you meet the manual's definition of “severe use,” take it in for changes more often; otherwise follow the interval, too.
Step up, not down in service rating. That API (American Petroleum Institute) issues a new service rating every few years, and with each one makes issues improvements that help with modern engine issues like sludge control, emissions, turbocharger protection, and ethanol-containing fuels. The current standard is SN (introduced in late 2010). All SH and earlier is considered obsolete, while SJ, SL, and SM are for 2001, 2004, and 2010 model-year vehicles or earlier, respectively. The bottom-line rule: If in doubt, you can use a newer standard in an older car, but don't use an older standard in a newer vehicle.
Consider temperatures, only if they're extreme. The API recommends that if outside temperatures are hitting lows below zero degrees Fahrenheit, you should probably move to a thinner oil, like 0W-20, 0W-30, 5W20, or 5W30; while in some very hot conditions you might want to go with a thicker oil. Again, check your owner's manual (or the official service manual) for the last word.
High-mileage engines have special needs. Yes, they do, and here's where high-mileage motor oils from well-known brands have their place. They often fully meet the requirements yet they also have slightly higher viscosities (they're thicker), a few more anti-wear additives, and seal conditioners that help give hardened seals some of their flexibility back (to help slow leaks).
Consider the brand. Just as with gasolines, formulation does vary, and quality varies, within what's permissible by standards and specifications. If you squirm at the thought of pouring the batch of oil that meets minimum spec but missed the big-brand quality cutoff into your car, then there's your answer: Stick with brands you know and trust.
Synthetic oils, blends, or mineral? Synthetic oils are engineered with a more complex combination of additives. Oil companies may try to convince you in advertising that these oils are better, but the more useful piece of advice is that they're better for some kinds of engines. They do in some cases stand up better to extreme heat and hard use, which is why they might be a good pick for a high-performance car or a tow vehicle. Here we go back to the advice of, go with what's recommended. If your car was delivered with a fill of synthetic and it's recommended, keep using it. Otherwise, they probably won't provide measurable extra protection for the cost.
So, to sum: Read your owner's manual. Then if in doubt, ask your mechanic for further advice based on the kind of driving you do and the condition of your engine. And check your oil every second or third fuel fill.