By contrast, synthetics are "designer" oils, chemically assembled or synthesized in labs from homogeneous low-weight molecules into heavier molecules with a chemical structure optimized for reduction of friction in specific applications. Synthetic oil molecules have a uniform size and chemical performance, resulting in an extremely stable product with highly predictable performance. Synthetics are entirely free of undesirable impurities like wax and ash. All synthetics are more expensive than conventional motor oils due to the complexity of the manufacturing process.
Synthetic oil manufacture begins with the production of pure ethylene gas from crude petroleum or natural gas. Ethylene is synthesized into homogenous light-weight hydrocarbons that are then polymerized to achieve thicker polyalphaolefin synthetic base stocks of heavier molecular weight. Synthetic base stocks also contain pure esters, which are essentially acid/alcohol compounds fully compatible with essential oil additives that are vital to the performance of modern motor oil in an automotive engine. Esters must be carefully blended with polyalphaolefins (which are thermally stable over a wide range but not particularly compatible with essential additives).
Specific measurable results from careful testing prove that synthetics are superior in the lab to conventional oils. Synthetics are clearly also great performers in the real driving environment. Unfortunately, it can be difficult or impossible to quantify the exact advantages of synthetic in a particular vehicle-especially on lightly-stressed stock factory engines in ordinary driving conditions where modern, high-quality mineral oils work quite well. It can be a little like a person trying to quantify the benefits of wearing sunscreen indoors.
Whether a synthetic lubricant will actually make a difference in the case of your engine all depends. How stressed are critical components on your engine such as crank bearings, rings, wrist pins, turbine bearings? How much thermal loading must your engine endure? How dangerous or expensive would it be if your engine failed catastrophically? In your case, synthetic could be overkill.
But do you really want to find out? In fact, the newest 100-percent synthetics have produced dramatic results in long-term-durability test engines, logging 200,000 miles with insignificant wear. Synthetic oils are so good that race engine builders are now virtually all using synthetics.
Why Synthetic Oils are BetterSynthetics are better both for what they contain and what they lack. They contain none of the traces of wax or ash of which conventional mineral oils cannot feasibly be 100 percent-free for economic reasons-impurities which accumulate on engine parts as the lighter fractions of mineral oil easily vaporize or are consumed in the combustion chamber, leaving thicker hydrocarbons and impurities behind.
With their tightly coherent molecular structure, synthetics also have inherently better resistance to thermal breakdown at high temperatures. Synthetic oils also flow better at particularly low temperatures (-60F vs. -40F). Synthetics typically require no pour-point depressants for cold starts and little or no VI-improver to maintain viscosity at high temperatures.
Whereas conventional oils begin to actively decompose into vapor and sludge at temperatures in the 340-450F range (which can happen in piston rings and turbocharger bearings), synthetics continue to lubricate critically hot parts without degrading. Synthetics are far more resistant to long-term breakdown and thickening via repeated "cooking" under heavy, hot loading over long intervals.
In the lab, synthetic performance advantages include wider-range viscosity index without VI improvers, lower ash content, higher flash point, lower boiling point, and lower pour (freezing) point.