Chapter Four – Conventional vs Synthetic Oils.

So far, we have been talking about engine oils in a very general sense, focusing mostly on the viscosity/temperature relationship and how this has changed to include a complex mixture of base oils and viscosity modifiers. But we also need to talk about some of the differences between Synthetic Oils and Conventional oils. We will not talk about the chemical differences, but rather some of the functional differences.

You will often see high performance cars recommend synthetic oils only in their owners’ manuals. People equate synthetic oils as high performance oils. There many of great benefits to using a synthetic oil over a conventional one. They typically take longer to oxidize, which means the oil change interval can go longer. They also can do a better job of maintaining the right operational viscosity as the temperature changes, they don’t thicken as much at lower temperatures which means greater flexibility in meeting the oil grade targets needed by the engine manufacturer. They are also more expensive and might be overkill for the average person driving to and from work, getting groceries and taking the kids to soccer practice and school.

Synthetic oils are different from conventional oils. One of the big differences is in their natural ability to maintain a similar viscosity as the temperature changes. In a conventional oil blend that meets 10W30, if you were to swap out the conventional base oil with a synthetic 1:1 without making any changes to the ratios or viscosity modifier you might end up with a 0W30 or a 5W30. That is because synthetic base oils do not thicken as much and so it would have better cold temperature performance. This also means that it will be lighter at start-up which means less wear and less wasted energy. Having this greater flexibility also means that the oil maker can change the blends to make higher performing products that allow for new engine technologies as well, for example, having a robust oil that meets the regular engine needs but can also help with a turbocharger which runs at much higher speeds and temperatures than the rest of the engine components. When a turbocharger is shut down hot, sometimes excessive oxidation can cause coking – this may be operator error, or a design flaw in the oil flow on the turbo. Oil marketers can use synthetic oils to help mitigate this issue.

At temperatures below zero you may not be able to start your car with mineral oils while the synthetic oils may be used to -40°F or -50°F. An excerpt from the web about Mobil 1 oils: They compared a 5W-30 synthetic Mobil 1 oil to a mineral based 10W-30 and a 10W-40 in ice cold conditions. The engine turned over at 152 RPM with the synthetic 5W-30 Mobil 1. The 10W-30 and 10W-40 mineral oils turned over at 45 and 32 RPM respectively. Neither of the engines using mineral oils started.

Start-up temperatures are not the only reason to use synthetic oil. Do you remember how we talked about oil thickening over time while it is being used? This is caused by oxidation. Oil, exposed to heat and air goes through a chemical reaction that creates oxidation particles which makes the oil thicker. Some of these get filtered out with your oil filter, some stays dispersed in the oil and changes the oil color to black, some of it gets left behind on engine components in the form of varnish and sludge. The best way to combat oil oxidation is to change your oil regularly. That said, synthetic oils not only are better at maintaining viscosity as the temperature changes – they are also more resistant to oxidation and volatility. This means that in general a synthetic oil can run longer oil drain intervals, in more harsh conditions than their mineral oil counterparts, such as prevention coking in some turbos. For some people this is an important factor, for others it might be overkill. Whatever you choose – make sure you follow your owner’s manual recommendation and match the type of oil you buy to the oil drain interval you follow.

Most synthetic and conventional oils are compatible with each other, so just because you start using synthetics does not mean you can not switch back if you want. Some people switch back and forth all the time and there normally is not any issues. The idea that once you choose synthetics you have to stick with it is a major myth that started when synthetics first came out. Both conventional and synthetic oils have come a long way since then.

You do not have to use synthetic oil, but there can be some real advantages to doing so. There are lots of people use synthetic, just like there are a lot of people who do not. It also does not really matter which brand you choose either, because there is a lot of oil manufacturing competition, which benefits all of us.  Some car manufacturers like you to use a specific brand (or their own special branded product) because they test and design their engines around those products. It does not mean that those brands are better, especially because lots of brands meet the same specifications (like the API specifications or an OEM spec such as Dexos1). If you are looking for a good oil to use first check your owner’s manual, then make sure you pick the right viscosity grade and do not be afraid to choose something that has better cold temperature performance because that will help with better startup and reduced energy consumption. Learn about the different specifications and applications oils are designed for, then pick a brand that makes you comfortable.

Chapter Three