Synthetic Oil: Is it Good or Bad for Older Cars?

Posted on: 27 January 2016

The next time you take your car to your local lube shop for a tune-up, there's a good chance your mechanic might suggest you switch from conventional oil to synthetic oil. But while synthetic oils are the new standard for a broad range of new vehicles, conventional oils are still de rigueur for many older vehicles. So is it worth it to make the switch from conventional to synthetic oil in your older car, truck or SUV? The following takes a look at the ins and outs of such a switch.

Understanding the Good

There are plenty of advantages that synthetic oils offer over their conventional counterparts. For starters, synthetic oils tend to perform better at both lower and higher temperatures. This not only gives your engine greater protection during start-up, but it also reduces the wear and tear commonly experienced during stop and go traffic as well as extended driving.

Unlike conventional oils, synthetic oils don't break down under extreme heat and pressure, leaving them less likely to leave behind sludge deposits. This can improve the longevity and fuel efficiency of your engine.

Understanding the Bad

Synthetic oils used to get a bad rap for causing leaks in older engines. As it turned out, the earliest synthetic oils didn't quite interact with seals and gaskets the same way that conventional oils did.

Most conventional oil formulations actively condition various seals and gaskets, allowing them to not only remain flexible, but also swell enough to close off most potential leaks. In addition, petroleum-based oils often leave behind deposits that often plug up gaps where oil leaks would have occurred. In contrast, synthetic oil blends of the 1970s and 1980s, commonly formulated using polyalphaolefin (PAO) base stocks, didn't have the right blend of additives to allow conditioning of the seals. The end result was often shrunken, dried seals that allowed synthetic oil to leak.

Thanks to years of consistent improvements, today's synthetic oils have come a long way from those days. In addition, modern seals used for engine repairs and rebuilds are nowadays designed to be compatible with synthetic oils. Nevertheless, many synthetic formulations still contain detergents that often strip away sludge deposits left behind by conventional oils, leaving an older engine more vulnerable to leaks.

There's also the common belief that synthetic oils are "too slippery" to be of use in some older engines, leaving them vulnerable to bearing wear and other internal damage. While synthetic oils are typically thinner and have higher lubricating properties than their conventional counterparts, there's little to no evidence to suggest that "slippery" synthetic oils are a poor choice for older engines.

Can You Switch Back?

A surprisingly common myth is that once you've switched from conventional to synthetic oil, it's nearly impossible to switch back. That may have been true during the early days of synthetic oils, but today's oils are so compatible with one another that such a switch winds up being relatively harmless.

If you do decide to switch back to conventional oil, however, it's still a good idea to completely drain your engine of its synthetic oil prior to filling it back up with a conventional blend. Although most semi-synthetic oils and the latest pure synthetic blends can exist happily with mineral-based conventional blends, pure synthetic oils based on polyglycol lubricants have no compatibility with conventional oils.

If you're not quite ready to give up on synthetic oils, you can bridge the gap between synthetics and conventional oils with semi-synthetic blends. Made from a combination of mineral-based oils and synthetic base stocks, semi-synthetic oils offer many of the same benefits as fully synthetic blends, but without the drawbacks that come with many synthetic oils. Learn more about your options by contacting companies like Big Mechanic.