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The "right" oil
Lubrication is what keeps expensive parts from wearing each other out. For example; Main bearings last hundreds of thousands of miles, as long as there is a layer of oil between them and the crank. Remove the oil and the bearings will quickly wear out.
Some oils are better than others, but many people don't have the foggiest idea what's the best brand and which weight to use. Some people say heavier oils are best, others say lighter, while others say to stick with straight weight.
Here's a simple rule of thumb that you may wish to employ when you have no idea what to use, and it works with many things other than oil - just follow the manufacturer's recommendation. If they say to use a particular brand, use that brand. Manufacturers have mechanical engineers on staff whose sole job is to know what's best. If that voice in the back of your head has you convinced your manufacturer is gouging you, you may want to consider swapping manufacturers. I mean, there should be some trust between the retailer and consumer, right? For me, it's simple. I'm an ex-Porsche owner who drives a Mercedes-Benz. Mobil1 is the factory fill for Mercedes-Benz and Porsche, so Mobil1 it is. Besides, Mobil1 is the factory fill for Bentley too, and Aston Martin, along with the Corvette, the Viper, the SRT-8, and a long list of others.
If you'd prefer a technical answer, first lets review the basics. Lubrication is dependant on flow. Viscosity, as it's measured in motor oil, is a measure of a fluid's resistance to flow, or it's "thickness". That "thickness" is quantified in centiStokes (cSt), which was named after Stokes Law for Friction. Motor oil thickness is temperature dependant. The normal operating temperature for motor oil is 100°C. So, that brings us to the logical question - what's the optimum thickness for motor oil at it's normal operating temperature?
Attached are two Mobil1 product data sheets from the Exxon Mobil website. One for Mobil1 0W-40 and the other for Mobil1
5W-40. At 100°C, Mobil1 0W-40 is 14 cSt. Mobil1 5W-40 is 14.8 cSt. Both 14 cSt and 14.8 cSt are fine. If the motor oil
in all automobile engines was always in that range, there would be no wear, and those engines would outlive most of us.
Now look at the cold start ratings. 0W-40 is 78.3 cSt. 5W-40 is over 100 cSt. Both are too thick for proper lubrication.
That's why most engine wear occurs during cold starts - the motor oil is too thick to properly lubricate. Ever
wonder how some taxi drivers put a half million miles on a single engine? The answer is right here - they never cool
down. Eliminating cold starts, cuts out a ton of wear. This is also why engine builders insist that engine loads be
kept at a minimum until the oil temperature is up to normal operating temperature.
Some people worry about oils having been recently reformulated. I've read on a lot of forums where people are concerned about zinc having been removed. For Mobil, that active ingredient is phosphorus. For oils and additives that meet the new ILSAC GF-4 specification, the phosphorus levels for the oil must be less than 800 ppm. The phosphorus levels were reduced to protect the emissions equipment. Engine manufacturers worked with ISLAC and are convinced that the new level of phosphorus will protect both new and older engines. Am I convinced? I only know what they tell me. I'm not worried about it though. That's because Mobil1 0W-40 doesn't meet the new specification. Mobil1 0W-40 has 1000 ppm of phosphorus. Those who are truly worried can use Mobil1 5W-40. Mobil1 5W-40 has 1300 ppm of phosphorus. Of course, people who use 5W-40 will have cold start and other considerations. Those who are convinced they need as much protection as possible can use Mobil1 Racing 4T. That's a motorcycle oil with 1600 ppm of phosphorus. One downside to using these other oils is they don't meet the Mercedes-Benz' 229.5 oil specification. Aside from killing the catalytic converter, going with one of these other oils may introduce other problems.