Is it okay to switch from synthetic to conventional oil

Myth #1: The “W” in 10W-30 stands for “weight.”

The numbers in a multi-grade rating represent the oil’s viscosity, or thickness. The higher the number, the thicker the oil. The best oils are a happy medium; neither thick like sludge nor thin like water.

Because oil viscosity changes with temperature, the multi-grade rating gives you both the hot and cold viscosities. 10W represents the oil’s viscosity rating for winter use, according to a rating system developed by the Society of Auto Engineers. And that’s why the “W” in 10W-30 stands for “winter.” Find the right oil viscosity for your vehicle with the Cenex lubricants recommendation tool.

Myth #2: You should change your oil every 3,000 miles.

Oil chemistry and engine technology have evolved tremendously since the days of the 3,000-mile oil change. The majority of vehicle manufacturers now recommend vehicle owners change their oil every 7,500 to 10,000 miles, based on a normal maintenance schedule. Why the change?

Synthetic oils, such as Maxtron® PCMO, are helping to stretch the time between oil changes. The improved oils provide superior anti-wear protection while maximizing fuel economy.

Also, oil life monitoring systems, which notify the driver when an oil change is needed, are becoming the standard in many new models. Instead of using the standby miles driven method, the technology monitors engine revolutions, operating temperatures and other factors to optimize the change interval selection.

Refer to your owner’s manual for your vehicle manufacturer’s oil change recommendation.

Myth #3: Synthetic engine oils can wear down seals in an engine and cause leaks.

This is an often-cited myth. In fact, if your seals and gaskets are in good condition, synthetic oil will not leak in your engine. Synthetic oil has not been shown to deteriorate engine seals or gaskets. But it might find an existing leak. The smaller molecules of synthetic oil are able to pass through very small cracks and crevices that the larger molecules of petroleum-based oil cannot. Eventually, those small cracks and crevices can lead to bigger problems — with or without synthetic oil.

Myth #4: My engine will benefit if I use supplemental additives.

Adding commercially available additives to your oil is unnecessary, as reputable motor oils will be already formulated with additives to ensure optimal engine performance.

Additional additives may dilute the effectiveness of the oil or even upset the oil chemistry. Refer to your owner’s manual for information about oil additives for your vehicle.

Myth #5: Once you use synthetic oil, you can’t switch back to conventional oil.

Switching between synthetic and conventional oils will not cause any damage to an engine. In fact, synthetic blends are a mixture of synthetic and conventional oil.

Click here for more information on Cenex engine oils. Find the Cenex oil that’s right for your vehicle with our lubricants recommendation tool.

Spread The Word

Although most of today's new cars, trucks and SUV's have synthetic oil inside their engines, there are still a few that utilize conventional motor oil as their primary source of lubrication. A commonly asked question here at YourMechanic.com is whether or not you can switch between regular and synthetic motor oil when you have your oil change completed.

The truth is - this is not a cut and dry, yes or no answer. In fact, depending on your individual application, the swap from conventional to synthetic or vice-versa may cause more harm than it's worth. In order to simplify the equation and to provide you with facts so you can make an informed decision, let's review some of the facts about oil changing with synthetic and conventional oil sold in the United States today.

What is Synthetic Oil?

Synthetic oil is made from chemical compounds that contain some petroleum elements combined with highly refined crude oil, organic, and inorganic compounds. In addition to synthetic oils, there are also synthetic blends that combine synthetic oils with traditional petroleum-based oils.

Synthetic motor oils were developed to address a major problem all combustion engines deal with each time they are started: oil and solvents do not mix well together. Engine oil is designed to lubricate moving parts inside the engine, especially around the combustion chamber. However, most fuels are petroleum based and are solvents, which literally wash away conventional oil which coats components.

Lubrication is especially important during start-up, as up to 75% of engine wear occurs as the engine warms up. Synthetic motor oils like Castrol GTX Magnatec provide a protective layer of thin lubrication on metallic components so they maintain lubrication for longer periods of time. As such, most synthetic oils have distinct advantages over regular motor oil, including:

  • Better high and low viscosity performance
  • Decreased evaporation
  • Resistant to oxidation and sludge issues
  • Improved lubrication during extreme cold weather
  • Improved horsepower and torque
  • Increased fuel economy

Synthetic oil typically lasts longer than conventional motor oil, which can reduce overall costs or at least help justify the higher price tag that comes with synthetic oils. For example, a person might change his or her oil every 3,000 miles with regular oil and only every 5,000 miles with synthetic oil.

Switching to Synthetic Oil from Conventional

When synthetic oil was originally developed it was meant to be used only in engines engineered to be specifically compatible with it. Older synthetic oils used esters, which are chemical compounds mixed with alcohol, and were harder on the components, including engine seals and gaskets. The esters would cause wear and create oil leakage, and potentially overheating problems. Today’s synthetic oils use less alcohol compounds, and engine gaskets and seals are made to withstand synthetic oils.

In general, there are three primary benefits to switching from conventional to synthetic oil:

  • To reduce oil change intervals
  • To remove carbon deposits on moving internal engine components (like cylinder head valves)
  • To extend engine life

As you made the switch from conventional to synthetic, it is recommended to do this progressively. Here are a few tips to consider:

  • For the first oil and filter change, switch from conventional to conventional/synthetic blend. Continue with synthetic/conventional blend for at least two other oil changes.
  • Always replace the oil filter anytime you change engine oil.
  • On the third oil change, switch from the conventional/synthetic blend to full synthetic.

The one thing you do not want to change is the recommended oil weight or viscosity. If the above process is followed, it should be safe to switch from regular to synthetic or use a synthetic blend as long as you use the same weight of oil.

Concerns About Switching to Synthetic Oil

Most newer model vehicles will adapt to the change with no problem. However, older models with high mileage may not adjust to the change. Their engine seals are likely to be thinner and worn, and you may find that they start burning oil as it seeps into the combustion chamber. Castrol EDGE High Mileage is a synthetic oil specifically designed for engines with lots of miles, but it is important to consult your owner’s manual or ask a trusted technician before making the switch in your vehicle.

No matter what type of oil you use, regular maintenance with oil changes is essential to extending the life of your engine. Follow the guidelines by the manufacturer or ask the technician how often you should have your oil changed based on the make and model and how the vehicle is used.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Can you go from synthetic oil to conventional?

When it comes to doing oil changes, switching between synthetic and conventional oil is perfectly okay. Despite the oil myths, both oil types are compatible with each other – no engine flush needed. So, simply making the switch will not cause any damage to your engine nor impact your travels.

What happens if you put conventional oil instead of synthetic?

Conventional oil, while cheaper than synthetic, is less refined and can lead to more engine sludge and gunk build-up down the road.

Is it OK to switch oil types?

Those rumors are mostly myths that have no basis in reality. So long as you do it right, it is perfectly fine to change oil type and improve your engine's protection against friction and overheating. Many people also change oil viscosity to a lower weight for cold wintertime travels and hot summertime heat.