How to Choose the Best Motor Oil

Brian Jones

January 13, 2026

8 min read

Brian Jones

January 13, 2026

8 min read

Changing your car’s motor oil - opens in new window or tab. yourself can save a lot of money. It’s a simple task, but you might be uncertain about how to choose the right engine oil and what your vehicle requires. This guide provides the answers.

Types of Engine Oil

A five quart jug of Castrol GTX Classic conventional motor oil. — Castrol GTX Classic conventional motor oil is a solid choice for vintage engines.

Back in the day, every car used conventional motor oil - opens in new window or tab.. As the most basic option, it offers a standard level of protection and lubrication at the lowest price. However, you need to change conventional oil more frequently, sometimes as often as every 3,000 miles. Conventional oil is made directly from crude oil that’s refined and blended with additives. Some older engines can only use conventional oil.

On the other end of the spectrum is full synthetic motor oil - opens in new window or tab.. Synthetic is composed of man-made chemicals to provide better protection and lubrication. While this oil is more expensive than conventional, some manufacturers allow for 10,000 miles between synthetic oil changes, reducing the cost per mile. Many vehicles, especially high-end models, require synthetic oil exclusively.

Mid-range synthetic blend oils - opens in new window or tab. combine the properties of conventional and synthetic oils. If you want added protection without the cost of full synthetic, a blend is a solid compromise.

Manufacturers also offer high-mileage motor oils - opens in new window or tab.. Typically, these are formulated for cars with over 75,000 miles. Special additives help prevent oil leaks, protect against engine wear, and prolong the life of the oil. The price is not much different from standard-mileage oil, and the increased viscosity of high-mileage oil provides better lubrication for worn-in engine parts. High-mileage oil is well worth considering for your older vehicle.

When you change your oil, you’ll need to change your oil filter - opens in new window or tab. too. Choose a filter that matches the change interval of your oil. It doesn’t make sense to use 10,000-mile oil with a filter rated for 3,000 miles.

Can you mix different types of oil?

If your vehicle is low on oil, you can add conventional oil to synthetic in a pinch, if both oils have the same viscosity. Mixing oils diminishes the synthetic oil’s performance. You won’t be getting your money’s worth out of the synthetic oil, and you’ll likely need to change the oil sooner.

Choosing the Best Oil for Your Vehicle

A vintage 1963 Chevrolet Owners Guide displayed on a cardboard background. — The owner's manual is the most reliable source for engine oil specifications.

To find the best engine oil for your vehicle, start by checking the owner’s manual. You should find details on the oil viscosity and type (conventional or synthetic) required for your engine. Never use an oil that doesn’t match the manufacturer’s recommendations.

Oil viscosity describes how fast the oil flows. The manufacturer will list a specific viscosity for your vehicle as a two-part number with a W in the middle—for example, 5W-30. This number will appear prominently on the label. Always stick with the recommended viscosity, as that’s what works best in your engine.

If your manual specifies conventional oil, you can choose to use conventional, synthetic, or blend, based on your preferences.
Low-mileage engines that aren’t driven in extreme conditions may be fine with conventional oil, though you’ll need more frequent oil changes.
You may consider a synthetic blend for added protection at an affordable price.
If you need increased temperature stability (for vehicles that tow or haul heavy cargo) or you want longer oil change intervals - opens in new window or tab., consider full synthetic.
If the engine has more than 75,000 miles on it, you could also upgrade to a high-mileage oil for better protection.
Many automakers require full synthetic oil. If this is what’s listed for your car, never use conventional or synthetic blend since these might interfere with the way your engine works.

Best Motor Oil Brands

A five quart jug of 0W-20 Valvoline Advanced Full Synthetic Motor Oil. — Valvoline Advanced Full Synthetic Motor Oil is engineered for today’s turbocharged/direct-injected engines.

Amsoil - opens in new window or tab. may not be the cheapest option available, but it is a premium brand trusted by racers and automotive enthusiasts, and its products are blended and packaged in the United States. The Signature Series lineup is Amsoil’s top-selling full synthetic.

Castrol - opens in new window or tab. is a reliable brand that auto mechanics trust. The full synthetic formula is known as EDGE. Castrol also offers a conventional option called GTX.

Liqui Moly - opens in new window or tab. makes specialty synthetic oil that is recommended for many high-end European cars. With special additives included, this brand provides superior lubrication for longer engine life.

Mobil 1 - opens in new window or tab. is likely the first oil brand that comes to mind because it has become synonymous with reliability. Mobil 1 makes extended performance and high mileage oil options that are compatible with just about every automaker’s engines.

Pennzoil - opens in new window or tab. has made motor oil for more than 100 years, making it another trusted name. Pennzoil’s high-mileage variant is good for prolonging engine life, while the Platinum label indicates full synthetic oil.

Royal Purple - opens in new window or tab. may be better known for oil additives but also offers high-performance synthetic oil. This specialty manufacturer makes formulas for motorcycles, ATVs, and racing applications, in addition to oils for everyday driving.

Valvoline - opens in new window or tab. earned its reputation among racing enthusiasts but has motor oil options for every type of driver. Valvoline’s full synthetic oil promises to remove deposits from older engines and the company offers a variety of high-mileage oil formulations.

Best Motor Oil for Diesel Engines

While several brands make high-quality diesel oils, here are two of our favorites.

Mobil 1 Turbo Diesel Truck - opens in new window or tab. oil is a full synthetic option designed for heavy-duty engines. It is compatible with modern diesel truck engines, including those with exhaust gas recirculation (EGR).

AMSOIL Signature Series Max-Duty Synthetic Diesel Oil - opens in new window or tab. delivers six times more wear protection based on third-party testing. It is designed for extreme temperatures and hard use, but it’s one of the most expensive engine oil options available.

Best Motor Oil for High Mileage

A five-quart jug of Royal Purple HMX High-Mileage Synthetic Motor Oil. — Royal Purple’s HMX Synthetic Motor Oil gets the nod for high-mileage vehicles.

Castrol Edge High Mileage - opens in new window or tab. is often reviewed as the best high-mileage oil for the money. Phosphorus replacement technology helps to extend the life of a car’s engine and emissions system. Plus, Castrol claims the oil is good for up to 15,000 miles between changes. It can be used in hybrid vehicles, and it’s known for reducing oil leaks and burn-off.

Royal Purple 11748 HMX - opens in new window or tab. is often hailed as the best synthetic oil for high-mileage vehicles. The specially formulated mix includes zinc and phosphorus additives that reduce wear.

Best Synthetic Motor Oil

While all of the brands listed above offer quality synthetic oil, we highly recommend Mobil 1. The company first released a full synthetic motor oil in 1974, making it the first available for passenger cars and trucks. Even today, many racers rely on Mobil 1.

Best Conventional Motor Oil

We can’t say enough good about Castrol GTX. If you need a high-quality conventional oil, GTX is tried and true. It’s been available for many decades, and a high-mileage variant is available for cars with more than 75,000 miles.

Best Motor Oil Additives

A one-gallon jug of Lucas Oil 10002 Heavy Duty Oil Stabilizer. — If your engine always seems to be down a quart, Lucas Oil 10002 Heavy Duty Oil Stabilizer might slow down the flow.

The best engine oil additives can extend engine life, clean out sludge and deposits, or improve gas mileage. Some aim to stop small oil leaks, while others reduce friction. For a deep internal cleaning, engine oil flush - opens in new window or tab. can clear out sludge and contaminants from your engine.

ZDDP Plus is the best oil additive for high-performance engines - opens in new window or tab.. Zinc dialkyl dithiophosphate forms an anti-wear barrier between metal components to reduce friction.

ATP AT-205 Re-Seal is the best oil additive for stopping leaks. The exclusive formula restores dried-out or worn seals without harming moving parts or bearings. It’s safe for gasoline or diesel engines.

Lucas Heavy Duty Oil Stabilizer is the best oil additive to slow or stop oil burning. Containing 100% petroleum, this engine treatment lowers oil temperature by reducing friction, extends the life of the motor, protects against corrosion, and eliminates dry starts. It can also re-lubricate seals and bearings.

Other Oil Change Supplies You’ll Need

Now that you know how to choose your motor oil, check your oil-change supplies. With eBay, you can order everything in one place and save money. You’ll need an oil filter wrench - opens in new window or tab. ($10 to $20), an oil drain pan - opens in new window or tab. ($5 to $25) and an oil funnel - opens in new window or tab. ($3 to $10). Spending money on the right tools and equipment now will help you save money every time you change your oil yourself.

About the author

Brian Jones

Brian worked for several decades as an ASE Certified Master Technician in dealerships before starting his used car lot. Today, he writes for top automotive publications including Motor1. In his spare time, he's dreaming of an escape to the country's best trails in an off-road beast.

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This article is meant to provide general guidance only. Automotive maintenance, repair, upgrade, and installation may depend on vehicle-specifics such as make and model. Always consult your owner's manual, repair guide for specific information for your particular vehicle and consider a licensed auto-care professional's help as well, particularly for advance repairs.