0W-20 vs. 5W-30: Is Thicker Engine Oil Better for Your Car?

A 5W-30 engine oil has a higher operating-temperature viscosity than 0W-20. Thicker engine oil can reduce oil consumption in some older engines because the higher viscosity limits the amount of oil passing through worn internal clearances. The effect depends on the condition of the engine and whether 5W-30 is an approved viscosity for that engine.

The initial differences in each of these two grades of engine oils begin with their SAE viscosity ratings. The “0W” and “5W” portion of the SAE viscosity rating describes how well an engine oil performs at lower temperatures. The “20” and “30” portion of the SAE viscosity rating identifies the viscosity grade at high temperatures. According to Mobil’s data for both its High Mileage formulations, at 100 degrees Celsius, Mobil lists a kinematic viscosity of 8.32 mm squared per second for 0W-20 and 10.71 mm squared per second for 5W-30.

The differences listed above may significantly influence the flow characteristics of an engine oil, its ability to reduce friction, the amount of fuel consumed by an engine and the amount of engine oil used by an engine. Regardless of the differences between the two engine oil grades, it should be noted that the proper grade of engine oil is dependent upon the specifications provided by the manufacturer of the engine.

0W-20 vs. 5W-30

0W-20 vs 5W-30 Both 0W-20 and 5W-30 are multi-grade engine oils. The first part of the grade indicates the low temperature viscosity, while the second number indicates the high temperature viscosity grade. 0W ratings have lower cold temperature viscosity requirements than 5W ratings. 20-grade oils also have lower viscosity at high temperatures than 30-grade oils.

Mobil’s data illustrates this well. The kinematic viscosity of their High Mileage 0W-20 was measured to be 8.32 mm2/sec at 100 degrees Celsius, whereas the kinematic viscosity of their High Mileage 5W-30 was measured to be 10.71 mm2/sec. The measured kinematic viscosities reflect the characteristics of these two particular formulations and do not represent all oils that carry the same SAE grade. The increased viscosity of 5W-30 will affect the flow rate of the oil within the engine and the behavior of the oil between the moving parts during operation.

In addition, the increased viscosity will produce more friction on the oil as it moves through the engine than 0W-20. The grade of viscosity alone does not tell you everything you need to know about how an engine oil performs or what its properties are. Performance standards like API, ILSAC, ACEA, and manufacturer’s specifications provide additional performance criteria for selecting a proper viscosity grade based upon those specifications.

The numbers describe viscosity. They do not indicate which oil is better for a particular engine.

Why Modern Engines Use Low-Viscosity Oil

The move toward oils such as 0W-20 is connected to modern engine design and fuel-efficiency requirements.

Oil has to circulate through passages, reach bearings and lubricate components while the engine is running. The resistance created by the lubricant also affects the energy required to move oil through the engine.

A lower-viscosity lubricant can reduce that resistance. Manufacturers can account for this when designing the lubrication system, bearing clearances and oil pump.

Fuel economy is one reason low-viscosity grades have become common in newer passenger vehicles. The oil still has to meet the required performance specification and provide protection under the temperatures and loads expected by the engine.

API’s current information also separates viscosity grade from oil-performance classification. Its documentation lists SAE 0W-20 and 5W-30 among the grades covered by API SP requirements.

Does Thicker Engine Oil Give Better Protection?

A higher-viscosity fluid will have a lower tendency to flow when heated. This property of thicker engine oil will have an effect on the amount of oil film that exists between two moving engine parts.

The level of engine protection provided by an oil can be influenced by more than just its viscosity. Other elements including the bearing clearance in a given engine (as well as how those clearances were designed and are maintained), oil pressure, temperature at which the oil is operating, pump capacity, passages used to carry the lubricating oil throughout the engine, and engine load will also affect the overall performance of the engine’s lubrication system.

Chemical formulations in the oil contribute to how well it protects against wear, controls deposits, and resists oxidation. Additional information is provided by the performance classifications. Requirements related to timing chain wear, low speed pre-ignition, deposits and sludge are included in API and ILSAC standards.

Therefore, while a 5W-30 may appear to be better than others due to its higher operating temperature viscosity, it is not.

What Changes as an Engine Accumulates Mileage?

Engine wear can alter the conditions under which oil circulates inside the engine.

Clearances between components can increase over time. An older engine may also develop oil consumption through worn piston rings, valve seals or other components. External oil leaks are another common source of oil loss.

A higher-viscosity lubricant can reduce oil consumption in some worn engines because thicker engine oil offers greater resistance to flow at operating temperature.

That does not make 5W-30 the standard choice for every high-mileage car.

Mobil sells high-mileage formulations in several grades, including 0W-20, 5W-20, 5W-30, 10W-30 and 10W-40. Its product data also shows different viscosity and performance characteristics for each grade.

A vehicle with 100,000 miles can therefore remain on 0W-20 when that grade is specified by the manufacturer.

Can Thicker Engine Oil Reduce Oil Consumption?

Oil consumption is one situation where a change in viscosity can produce a noticeable difference.

A higher operating-temperature viscosity can reduce the amount of oil passing through certain worn clearances. This can reduce consumption in some engines, and thicker engine oil can be one option when the manufacturer permits a higher viscosity.

The effect depends on the mechanical condition of the engine.

An engine losing oil through a damaged gasket or seal will continue to leak regardless of whether it contains 0W-20 or 5W-30. Internal oil consumption caused by worn piston rings is a different problem. A crankcase ventilation fault can produce another set of symptoms.

Changing viscosity can alter consumption without repairing the component responsible for the oil loss.

That distinction is important when deciding whether thicker engine oil is appropriate.

Does Hot Weather Make 5W-30 a Better Choice?

While the outside air temperature is a factor in determining the correct engine oil viscosity, it is not the only one. The amount of work an engine is doing (i.e. how many times a minute it is rotating) and how effectively the cooling system operates are two other factors which affect the engine oil temperature.

In addition, the speed at which you are operating your vehicle and the type of engine installed in your vehicle (i.e., whether it is cast iron, aluminum, etc.) all contribute to the overall engine oil temperature.

Therefore, while there will always be a difference between the outside air temperature and the engine oil temperature, there will not necessarily be a direct correlation.

In fact, some manufacturers may allow for several different types of engine oil to be used in a particular engine, with recommendations being made as to which viscosity should be used depending on the outside temperature. This may include thicker engine oil when it is specifically approved for the engine.

A similar engine could possibly be limited to fewer approved viscosities. Always refer to your Owner’s Manual to find out which motor oil viscosity is recommended for your vehicle. The American Petroleum Institute (API) suggests that all vehicle owners refer to their Owner’s Manual prior to using any of API’s motor oil categories.

What Happens During a Cold Start?

The first number in an oil grade becomes particularly relevant when the lubricant is cold.

A 0W oil has better low-temperature viscosity performance than a 5W oil. Both types of oils perform differently in terms of their behavior while the engine is being cranked cold; they also perform differently when tested at low temperatures to determine their SAE classification.

Once the engine reaches operating temperatures, the second number in the viscosity rating will describe the oil’s relevant viscosity grade.

Therefore, it would be incorrect to say that both 0W-20 and 5W-30 are just two different oils with different thicknesses.

The SAE J300 classification deals specifically with these rheological properties. It does not evaluate the complete performance of an engine oil.

Turbocharged Engines Need More Than the Right Viscosity

Turbocharged engines place high thermal demands on engine oil.

The turbocharger shaft operates at very high speed, and the lubricant around the turbocharger can be exposed to high temperatures. Oil formulation and performance standards therefore become particularly important.

The required viscosity varies between engines.

A turbocharged engine can be designed for 0W-20, 5W-30, 0W-30 or another grade. The manufacturer can also specify particular performance standards alongside the viscosity.

ILSAC GF-6A, for example, includes requirements related to low-speed pre-ignition, timing-chain wear and high-temperature deposits involving pistons and turbochargers.

The viscosity printed on the bottle is only one part of the specification.

Why the Oil Specification on the Bottle Matters

Two 5W-30 oils do not necessarily have identical performance characteristics.

The SAE grade identifies viscosity. API, ILSAC, ACEA and manufacturer approvals provide additional information about the oil’s performance and intended applications.

API’s current oil-category information lists performance requirements beyond viscosity, while manufacturer approvals can add requirements specific to a particular engine family.

This is particularly relevant when selecting oil for modern engines. Matching the viscosity while ignoring the required specification can result in an oil that does not meet the manufacturer’s requirements.

The correct bottle should therefore match both the required viscosity and the required performance specification.

Does 5W-30 Affect Fuel Economy?

The higher viscosity of 5W-30 at operating temperature creates greater resistance to flow than 0W-20.

That could lead to higher amounts of energy being used to get the lubricant to flow through the engine and could also result in increased friction loss (pumping) and reduced efficiency. Fuel-Economy Difference Variation The level of fuel economy differences will depend on a number of factors including the type of engine, the specific oil formulation used, the operating temperature and how you are driving.

Why Some Manufacturers Use Low Viscosity Oils It is common for manufacturers to select a low-viscosity lubricant for their engines that have been developed with a focus on fuel efficiency. The selection process for this lubricant takes place at the same time as the development of the mechanical components of the engine, not after.

When Does 5W-30 Make Sense?

Using a 5W-30 grade of motor oil is appropriate as long as it has been approved for your particular type of engine. A 5W-30 motor oil may also be beneficial for an older engine which has begun to burn more oil than normal if the manufacturer allows the use of a thicker (higher) viscosity. In some of these cases, thicker engine oil may reduce oil consumption. Some engines which have developed larger gaps (clearances) inside them may experience less burning of their engine oil as a result of using a motor oil with a higher operating temperature viscosity.

The total amount of miles on a vehicle are not sufficient grounds to use a different grade of motor oil. There is no engineering evidence to suggest that a thicker (higher viscosity) motor oil will offer greater protection than a thinner (lower viscosity) motor oil if a manufacturer recommends a 0W-20 grade and does not recommend a 5W-30 grade.

However, if both grades of motor oil have been recommended by the manufacturer, then you can select the correct grade based upon the temperature conditions under which the vehicle is operated, the condition of the vehicle’s engine and the recommendations found in the vehicle’s Owner’s Manual.

When Should You Stay With 0W-20?

Unless a different type of oil has been authorized by your vehicle’s manufacturer, an automobile that was built and rated to run on 0W-20 will need to remain on 0W-20. The need to stay on 0W-20 is especially true for newer vehicles with closer tolerances and lubrication systems designed specifically to operate with lower-viscosity oils.

The amount of miles you have put on your vehicle does not dictate what kind of oil should be used in it. Mobil’s own line of high-mileage products illustrates this concept by providing both 0W-20 and other heavier weight oils (5W-30, 10W-40) in its lineup.

What Should You Check Before Switching From 0W-20 to 5W-30?

Check the owner’s manual before making the change.

Look for:

• SAE viscosity: Confirm whether 5W-30 is approved.
• Temperature range: Check whether the manufacturer specifies different grades for different temperatures.
• Oil performance standard: Check API, ILSAC, ACEA or the manufacturer’s own approval.
• Engine-specific requirements: Turbocharged and other specialized engines can have additional requirements.
• Oil consumption: Determine whether excessive oil use is caused by wear, leakage or another mechanical problem.

The oil container should match the specifications listed for the engine, not simply the viscosity number.

Is Thicker Engine Oil Better for an Older Car?

An older engine can benefit from a higher-viscosity oil in certain circumstances, particularly when increased clearances are contributing to oil consumption. Thicker engine oil may help in these situations when the manufacturer allows a higher viscosity.

That does not make thicker engine oil a universal solution for aging engines.

A high-mileage, healthy engine that isn’t burning too much oil will have a different need for lubrication than an engine with ring/seal wear. The manufacturer’s recommended viscosity range is the limit in which a person could consider changing their engine oil.

If oil consumption has increased significantly, diagnosing the engine is more useful than immediately moving to a thicker lubricant.

0W-20 vs. 5W-30: Which Oil Is Right for Your Car?

The correct choice in the 0W-20 vs. 5W-30 comparison depends on the engine manufacturer’s specification.

5W-30 has a higher operating-temperature viscosity than 0W-20. That property can help reduce oil consumption in some worn engines and provides different flow characteristics under operating conditions. This is why thicker engine oil can sometimes be considered for an engine with increased oil consumption.

0W-20 has a lower high-temperature viscosity and can reduce resistance to oil movement. Engines designed around the grade take that characteristic into account when the lubrication system is developed.

Neither characteristic makes one grade universally superior.

The manufacturer’s approved viscosity and oil-performance specification should come first. Engine condition, climate and operating conditions can then be considered within those specifications.

The use of a higher-grade engine oil (5w-30) in place of what the manufacturer recommends for your engine oil viscosity (0w-20) is not a reasonable method to maintain your vehicle’s engine. There are a few situations, though, where you could justify the use of a thicker engine oil (5w-30). One situation would be if the manufacturer approves it as an acceptable alternative.

Another situation would be if your engine has experienced certain types of oil consumption issues that could be remedied by using a thicker engine oil. There really is a distinction between the two grades. The concept that thicker engine oil will always perform better is inaccurate.