Best Motor Oils For 2021

Best Motor Oils For 2021
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Think of motor oil as cheap insurance. Regular oil changes prevent the buildup of carbon and sludge, extending engine life. Guarding against thousands of dollars in damage for the relatively tiny cost of oil changes is a no-brainer, but how does that work? And what makes one engine oil better than the rest?

Oil creates a protective film between an engine’s moving parts, which rotate or move thousands of times every minute. In this razor-thin space where every molecule counts, an engine oil’s distinctive additives enable oil to give protection with minimal resistance. The less drag on the engine’s moving parts, the more power and fuel economy are realized. For the oil itself, the longer it maintains its chemical stability, the longer it’s able to effectively protect against friction. 

Synthetic and conventional oil both start life as crude oil. Conventional oils use additives to achieve the desired viscosity range, but when those additives deteriorate, the oil’s ability to adapt to changing temperatures is diminished. Synthetic oils are created by breaking down crude oil on the molecular level and rebuilding them to a specific innate and uniform structure, which nearly eliminates deterioration. Synthetic tends to stand the test of time much better than conventional oil. However, because engine oil naturally absorbs harmful particles such as dirt, carbon and metal shavings, it’s still important to regularly change the oil and filter.

Each oil brand closely guards their proprietary chemical formulas as a trade secret, with promises to protect longer, better and across a wider range of environmental conditions. The one that’s right for your vehicle can vary just as much, as different engines, driving habits, and vehicle uses call for different solutions. That said, many manufacturers specify a recommended brand and viscosity, typically called the oil weight. We chose five outstanding engine oils known to deliver reliable protection at a great price. Each is suited for a specific application.

Best Advanced Synthetic Motor Oil: Mobil 1 Extended Performance

Why We Picked It: 

As synthetic motor oils go, Mobil 1 is the industry benchmark. Well-regarded for its detergent qualities, Mobil 1 has been the factory-fill choice for high-performance engines for decades. The Extended Performance formulation is designed to protect for up to 20,000 miles under optimal driving conditions. Prices have steadily fallen as it’s become more popular, making Mobil 1 Extended Performance our top choice for the best overall value among engine oils.


  • Demonstrated track record of dependability
  • Factory recommended in many cases
  • Low price, extended service interval


  • More expensive than other synthetics
  • Even longer lasting annual protection formula now discontinued
  • Stick to and trust your maintenance schedule rather than relying on the formula

Best Budget Synthetic Motor Oil: AmazonBasics Full Synthetic High Mileage Motor Oil

Why We Picked It: 

Yes, Amazon does sell its own brand of synthetic motor oil, and it’s a cost-effective solution most users like. Though it isn’t a familiar brand name, most viscosities sold under Amazon’s label conform to General Motors’ DexOS standard. Many automakers have adopted this standard as an assurance of an engine oil’s protective and detergent properties and DexOS-rated oils meet a host of engineering benchmarks and are monitored for quality. When ordering, look for the DexOS symbol on the front of the bottle to verify the oil meets this standard. We only recommend DexOS-rated oils.


  • Demonstrated quality
  • Long service life
  • Low price


  • Not all viscosities are DexOS-rated
  • Unknown brand
  • Not that much cheaper than name-brand synthetic oils

Best Conventional Motor Oil: Castrol GTX

Why We Picked It: 

As the cost of synthetic oil drops closer to conventional oil, remember that some engines are still better suited to conventional oils. Older vehicles or engines that have run on conventional oil for hundreds of thousands of miles may need the specific additives included in conventional oils to prevent leaking seals. Rotary engines in particular require conventional oil, and Mazda specifically recommends against using synthetic oil in models like the RX-7 and RX-8. Castrol GTX is a high-quality conventional oil that helps keep older engines healthy and, when it does enter the combustion chamber because of worn rings or seals, burns fairly cleanly, protecting spark plugs from premature fouling.


  • Reputation for quality
  • Keeps older engine seals healthy, burns cleanly if it does get past rings or seals
  • Formulated to protect against sludge


  • Doesn’t respond to temperature variations as consistently as synthetics
  • Shorter service life than synthetics
  • Limited number of weights available

Best Diesel Motor Oil: Shell Rotella T6 Diesel Engine Oil

Why We Picked It: 

Diesel engines often work harder, longer hours than their gasoline counterparts, whether it’s a truck towing a heavy load or a long-range diesel car driving for hours on end without stopping. Extended heat cycles, longer service intervals and the sheer expense of a diesel oil change make it important to choose a high-quality oil. Shell Rotella has a higher pour point than some other oils, the temperature at which the oil loses its flow properties, which means it’s less likely to leak from worn seals or older engines. One tip: for trucks that require large quantities, a bulk three-gallon pack isn’t always cheaper than buying individual gallons.


  • Strong reputation in agricultural and trucking industries
  • Higher pour point slows small leaks
  • Mail-in rebates often offer considerable savings


  • Buying the big sizes isn’t always cheaper than buying by the gallon
  • Higher pour point can impact flow in cold temperatures
  • Popular truck viscosities are pricey

Best “Get-it-Home” Motor Oil: Quaker State Synthetic Blend, $15

Quaker State Motor Oil, Synthetic Blend 5W-20 (5-Quart, Single Pack)

Why We Picked It: 

Sometimes, you just need to get home. For engine flushes or other situations where budget is the primary concern, Quaker State makes a synthetic blend that’s cheaper than even some conventional oils. Unlike no-name products, Quaker State is a well-known brand with consistent quality control standards and a staple in many auto dealers’ oil change specials. Synthetic blend oils deliver more consistent viscosity changes in response to temperature variations than conventional oil, suiting them to climates with moderate temperature swings. 


  • Name-brand quality and consistency
  • Budget price
  • Better suited to temperature changes than conventional oil


  • Bargain price only applies to certain viscosities
  • Not DexOS rated
  • Basic oil without additives geared toward high mileage applications


We specifically chose highly-rated and readily available motor oils that are compatible with a wide range of vehicle makes and models on the road today. Forbes Wheels considered the products that are the most accessible to consumers residing throughout the U.S. and selected five types of motor oil by considering a broad range of end-user ratings and professional evaluations, including our own experiences using these products. Each product is rated on quality, durability, vehicle compatibility, and protection from wear and sludge.

FAQs (Frequently Asked Questions):

How often should I change my oil?

Always follow the vehicle manufacturer’s recommendations as specified in the owner’s manual. Manufacturers may void a vehicle’s engine warranty if the maintenance schedule is not followed, even with extended performance oils. Many engines still consume oil between oil changes, so it’s vital to periodically check the oil level at the dipstick to monitor the oil level and color. Oil changes are cheap protection against inexpensive repairs, so when in doubt, err on the side of safety.

What oil is good for older or high-mileage engines?

High mileage formulations of conventional, synthetic blend and full synthetic engine oils contain additives which can condition seals, helping to prevent leaks, and also fight sludge. As engines age, piston rings and other internal components can seize up. Special detergent packages in high mileage oil blends help keep engine components moving freely, improving oil flow and lengthening the life of an engine.

What are the disadvantages of synthetic oil?

Cost used to be the biggest disadvantage of synthetic oil, but as automakers require the use of synthetic oil in most new modern vehicles, prices have fallen. Synthetic oil is generally better at protecting engines and retains its chemical properties longer  than conventional oil, but it doesn’t burn as well if it ends up in the combustion chamber, which can happen on older vehicles with worn seals or piston rings. While synthetic oil won’t degrade seals, it is thinner than conventional oil and may pass more easily through existing worn seals or leaks, appearing to exacerbate the underlying issues.

Can I mix synthetic and conventional oil?

Yes, in a pinch. Synthetic oils are compatible with conventional oils, so topping off with one when the matching oil is unavailable is okay. However, due to differences in additives that can react with each other, it’s wisest to select either synthetic or conventional oil and stick with it. Blending synthetic and conventional oils can lead to sludge or varnish over time.

Can I use a different oil viscosity than recommended by the manufacturer?

Always follow the vehicle manufacturer’s recommendations. Using a lighter weight oil than specified by the manufacturer will fail to fully protect against wear, while using a heavier weight oil than specified will overstress internal engine parts. Both can trigger expensive repairs, so it’s best to choose the engine oil specified by the vehicle manufacturer for your climate and usage.