Full Synthetic vs Synthetic Blend Oil (What’s the Difference?)

The engine oil section of an auto parts store is quite overwhelming. Not only do you have to decide between different oil weights, you also have to consider the difference between conventional, full synthetic, and synthetic blend oils.

How Important Is My Engine Oil?

Engine oil is one of the most important fluids in your vehicle, as it is critical to your engine’s operation. An engine cannot run for more than a few moments without oil before causing permanent damage.

If you see a red or amber oil light come on while you’re driving, pull over as soon as it is safe to do so and check the oil. You may have low oil pressure. If the oil level is low, add oil until the level reaches the “full” line on the dipstick.

Differences Between Full Synthetic and Synthetic Blend Oil

engine oil type

When you look down the engine oil aisle, look closely at each bottle to see which type of oil you’re buying. Here are three types of oil you will likely see.

1) Full Synthetic Oil

Full synthetic oil (often referred to as “synthetic”) is an engine lubricant that is created in a lab. Since the product is manufactured, the oil molecules are much more uniform in shape and size.

Synthetic oils tend to break down more slowly than conventional oils, and can last much longer in your engine. Synthetic oil change intervals range from 5,000 to 20,000 miles in extended use scenarios.

3) Synthetic Blend Oil

A synthetic blend oil is a cross between a synthetic oil and a conventional oil. Different synthetic blends have different percentages of each type of oil.

Different proportions of synthetic and conventional oil will give a synthetic blend properties that favor one or the other, with less of the drawbacks of that type of oil. A synthetic blend aims to be cheaper than a full synthetic, with more longevity than you’d typically see with a conventional oil.

3) Conventional Oil

Also called mineral oil, conventional motor oil is an engine lubricant that is created from natural crude oil. Traditionally, people have used conventional motor oil to lubricate the components of their engines, and this type of oil has been around the longest.

Conventional oil is often much cheaper than synthetic. Since the oil molecules come from natural oil, not all of the oil molecules are the same size. This type of oil tends to break down a bit more quickly than full synthetic. Common oil change intervals for conventional oil is around 3,000 miles.

How Often Should I Change My Oil?

oil change and tune up

Each vehicle and engine oil will have a different interval for how often you should change your oil. Not sure where to start? Here are some common oil change intervals for different types of oil and use cases.

Most vehicles that use full synthetic oil and are driven normally have oil change intervals between 6,000 and 10,000 miles. Some extended performance full synthetic oils are designed to last as long as 20,000 miles or one year, whichever comes first.

A synthetic blend oil can last anywhere from 5,000 to 7,500 miles. For people who aren’t comfortable with an extended oil change interval, this could be a great way to save some money on oil compared to full synthetic.

For Severe Use

first time track day questions

In severe use cases, most manufacturers recommend you change the oil every 3,000 miles. Some examples of severe use are operating the vehicle in dusty areas, running the engine hard (high load, high RPM), high city miles, or idling frequently. If you do any of these things, you may want to consider using a severe use interval.

Check the owner’s manual for your vehicle to know exactly which type of oil, viscosity, and oil change interval the manufacturer recommends. This is a great starting point and you can always adjust this interval later as needed.

Perform a Used Oil Analysis

used oil analysis

A used oil analysis (UOA) from a company like Blackstone Laboratories will be able to give you the most accurate oil change interval recommendation for your vehicle, based on your vehicle, engine, environment, and usage.

Blackstone will send you a container you can use to collect an oil sample. To collect the sample, catch a bit of oil from the oil pan in the provided container.

You want to try to catch the oil mid-stream, and the test is most accurate if the engine oil is at operating temperature. This allows any fuel to burn off that was introduced during a cold start. Don’t dip the container into the oil pan, as this will contaminate your sample.

If you pay for a total base number (TBN) test, Blackstone can give you an estimate for how many more miles you can go on that specific oil with that specific vehicle.

Why Is My Oil Dark?

used engine oil
Used engine oil from a healthy engine. Drained at 2,300 miles.

Oil changes color from amber to black as it picks up hydrocarbons from the engine and suspends them. This is a good thing, and it means the oil is doing its job. Oil will start to turn brown pretty much immediately after you’ve changed the oil.

Brown oil does not necessarily mean you need to change the oil again. If your oil is pitch black, it may be time for an oil change. Typically, it is hard to tell when you need to change your oil just by looking at or smelling the oil, unless the vehicle is way overdue for an oil change.

What Oil Should I Use?

Although there are many options at the auto parts store, try not to overthink the choice for your vehicle. As long as you’re following the recommended oil viscosity and the oil meets the necessary American Petroleum Institute (API) certifications, that choice should work great for you.

Different oils have different additive packages, but as far as protecting your engine from blowing up, most oils from the parts store will do the job just fine. Don’t be afraid of parts store oils, either. Many of these oils use the same or similar formulas you’ll find in the name brands (like buying a generic product at the grocery store).


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