Oil changes are one of the most common types of car maintenance, and they’re a bit divisive. Today, there are more options, and drivers must choose between conventional and synthetic oils. What’s the difference? Is it only that synthetic oil is more expensive, or is one better than the other? In the end, should you pay more for a synthetic oil change or stick to conventional oil?
How Engine Oil is Made
Though conventional oil and synthetic oil appear similar, they have very different origins. It is that difference that makes synthetic oils superior to conventional oils in a number of ways.
Conventional oil has a long history, much further back than the development of petroleum distillation in the 19th century. Scientists suggest several hundred billion tons of microbes may have lived and died long before dinosaurs. Vast deposits of microscopic life forms would convert to what we know of as petroleum, eons later.
First, oil drillers pull raw petroleum from wells deep in the earth. Then, at the oil refinery, crude petroleum is “cooked,” and it separates into “fractions” of differing density.
- C70+ High-density asphalt contains the longest hydrocarbon chains.
- C20-C50 Higher in the column, mid-density mineral oil has shorter hydrocarbon chains.
- C5-C10 Even higher in the column, low-density gasoline has even shorter hydrocarbon chains.
- C1-C4 Highest in the column, low-density flammable vapors have the shortest hydrocarbon chains.
That C20 to C50 range is where we get engine oil from, but not without additional processing. Further refining separates the oil into more fractions, base oils we would recognize as Grade 5 or Grade 30, for example.
Synthetic oil is “constructed” or synthesized from short-chain hydrocarbons, but this isn’t new. German chemists Franz Fischer and Hans Tropsch developed a process in 1925. Carbon monoxide (CO) and hydrogen (H2), at high heat and pressure, combine to produce long-chain hydrocarbons. Organic synthesis is another common method. Modern synthetic oil derives from ethylene (C2H4), propane (C3H8) or butane (C4H10), high in the refining column. Natural gas, or methane (CH4), also is used to synthesize synthetic base oils.
It took a long time for engineers to discover the benefits of synthetic oil. In the 1970s, only a couple of companies offered synthetic oil. Today, automakers ship most of their new cars filled with synthetic oil.
Additives are blended into the base oils to improve their lubricant characteristics.
To make it more useful at high temperatures, viscosity index improvers change how the base oil reacts to heat. The result is a “multi-grade” oil blend, such as “5W-30.” When cold, the oil flows like a thinner Grade 5, closer to a C20 hydrocarbon chain. As the oil heats up, additives thicken the oil to approximate a Grade 30, closer to C30, at 100 °C.
Other additives include anti-wear agents, detergents, foam inhibitors, corrosion inhibitors and pour-point depressants.
How They Perform Over Time
Synthetic oil outperforms conventional oil. To understand why synthetic oil is often a better option, we need to look at how they both perform over time. At its most basic, the difference in purity makes synthetic oil superior.
- Uniformity – The molecules in conventional oil are not uniform. The average hydrocarbon chain may be C30, but there may be chains at either end of the spectrum. The short C20 chains flow faster, while the long C40 chains flow slower. At high temperatures, this disparity becomes even clearer. This results in unpredictable lubrication and possible engine damage. The manufactured molecules in synthetic oil are more uniform. The average hydrocarbon chain may be a C30, with almost no variation. This uniformity maintains synthetic oil flow characteristics across the entire temperature range.
- Purity – Conventional oil comes from petroleum deposits containing other non-lubricant contaminants. Wax, sulfur, nitrogen and metals can interact at high temperatures, impacting lubricant performance. Synthetic oil comes from pure base stocks and contains no contaminants at all. This means there is nothing to cause unwanted reactions in the high-heat engine environment.
5 Reasons You Should Use Synthetic Oil
We have already gotten far too technical, though. What does all this stuff about chains and uniformity have to do with your next oil change? The easiest way to say it is to come right out and say it: Synthetic oil is better.
- Industry tests prove synthetic oil lasts longer. It doesn’t contain contaminants that can oxidize or develop sludge. Your engine will last longer.
- It’s less expensive to use synthetic oil. You can extend your oil change interval up to 15,000 miles by using a quality synthetic oil and high-capacity oil filter. You’ll spend up to twice as much to do a single oil change, but you’ll only change it one-third as often.
- By extending oil change intervals, you generate less waste oil. There is less chance for waste oil to contaminate the environment.
- Even at lower weights, synthetic oil improves fuel economy while protecting your engine. This reduces the emissions your vehicle generates.
- Synthetic oil does not depend on petroleum deposits. This reduces the pressure to drill for more oil.
When it comes to taking care of your car, making sure the engine runs its best is key. By choosing synthetic oil, you will spend a little more, but it’s the wisest choice for your engine, your wallet, and the environment.