10W-40 vs 20W-50 Motorcycle Oil Which One Should You Use
Choosing between 10W-40 and 20W-50 motorcycle oil can look simple: one is often recommended for cooler conditions, while the other is commonly associated with heat and heavier use. In reality, the correct choice depends on much more than the weather. Engine design, cooling system, operating load, manufacturer specifications, and wet clutch requirements all matter.
The numbers on the bottle describe how the oil behaves in standardized viscosity tests. They do not tell you which oil is universally better, and they do not replace the viscosity chart in your motorcycle owner’s manual.
Quick Answer
10W-40 generally meets lower-temperature starting and pumpability requirements than 20W-50, while 20W-50 remains more viscous at normal engine operating temperatures. Neither grade is automatically better. Use only a viscosity approved in your motorcycle owner’s manual, then confirm the required JASO and API performance classifications.
If you are still learning how viscosity, specifications, and product labels work together, start with our guide to reading a motor oil label. It explains why a familiar viscosity grade is only one part of selecting the right lubricant.
What 10W-40 and 20W-50 Actually Mean
Both 10W-40 and 20W-50 are multigrade engine oils classified under the SAE viscosity system. The first part of the designation describes low-temperature performance. The letter W refers to winter-grade testing, while the second number identifies the oil’s viscosity grade at higher operating temperatures.
- 10W-40: meets the requirements of a 10W winter grade and an SAE 40 high-temperature grade.
- 20W-50: meets the requirements of a 20W winter grade and an SAE 50 high-temperature grade.
- A lower W number generally indicates that the oil meets cranking and pumpability requirements at lower test temperatures.
- A higher second number indicates a more viscous grade at normal engine operating temperatures.
Important: 10W-40 does not mean the oil has a viscosity of “10” in winter and “40” in summer. Likewise, 20W-50 does not describe a temperature range from 20 to 50 degrees. These are standardized SAE viscosity grades, not outdoor temperature ratings.
SAE viscosity also does not tell you whether an oil is synthetic, conventional, suitable for a wet clutch, approved for a specific engine, or built with a stronger additive package. Those characteristics must be checked separately.
10W-40 Motorcycle Oil Explained
Compared with 20W-50, 10W-40 has a lower winter grade. Under the standardized tests used to classify engine oils, it must meet low-temperature cranking and pumpability limits at lower temperatures than a 20W oil.
In practical terms, this generally makes 10W-40 the more suitable of the two for cooler starts when both grades are permitted by the motorcycle manufacturer. Once the engine reaches normal operating temperature, it behaves within the SAE 40 viscosity range.
Where 10W-40 Is Commonly Considered
- Motorcycles operated across a broad range of seasonal temperatures
- Applications where the manufacturer specifically recommends SAE 10W-40
- Engines where easier low-temperature cranking and oil pumpability are important
- Modern air-cooled or liquid-cooled motorcycles designed around this grade
Lube Squad carries several motorcycle oils in this viscosity, including Everest 4T Motorcycle Oil 10W-40 and Petromerica 4T Semi Synthetic PLUS 10W-40. Product availability does not replace checking the viscosity and performance requirements for the specific motorcycle.
20W-50 Motorcycle Oil Explained
SAE 20W-50 has a higher winter grade and a higher operating-temperature grade than 10W-40. It is generally more resistant to flow during a cold start, but it also remains more viscous after the engine reaches normal operating temperature.
This is why 20W-50 is often associated with certain high-temperature, high-load, older, or air-cooled motorcycle applications. However, those associations are not a universal recommendation. The engine must be designed for the grade, and the manufacturer must permit it.
Where 20W-50 May Be Considered
- Motorcycles whose manuals specifically list SAE 20W-50
- Approved operation in sustained heat or under heavier loads
- Certain air-cooled engines designed for a higher hot-viscosity grade
- Applications where SAE 50 is included in the manufacturer’s viscosity chart
Available products include Everest 4T Motorcycle Oil 20W-50 and Petromerica 4T Semi Synthetic PLUS 20W-50.
10W-40 vs 20W-50 Motorcycle Oil Comparison
| Factor | 10W-40 | 20W-50 |
|---|---|---|
| Winter grade | 10W | 20W |
| Cold-start behavior | Meets lower-temperature cranking and pumpability requirements | Generally more resistant to flow when cold |
| Operating-temperature grade | SAE 40 | SAE 50 |
| Hot operating viscosity | Lower than an SAE 50 grade | Higher than an SAE 40 grade |
| Common association | Broad-use motorcycle viscosity and cooler starts | Approved heat, load, or specific air-cooled applications |
| Wet clutch compatibility | Depends on the JASO rating | Depends on the JASO rating |
| Correct choice | Use only when approved by the manufacturer | Use only when approved by the manufacturer |
The table compares viscosity behavior, not overall oil quality. A properly specified 10W-40 can be a much better choice than 20W-50 when the motorcycle was engineered for SAE 10W-40.
Which Motorcycle Oil Is Better for Cold Starts
Between these two grades, 10W-40 generally has the advantage during colder starts. Its 10W classification requires it to meet low-temperature cranking and pumpability limits at lower test temperatures than a 20W oil.
That matters because oil must move through the lubrication system soon after the engine starts. However, it would be inaccurate to assign one universal outdoor temperature limit to every motorcycle. Manufacturers account for engine design, oil pump capacity, clearances, and the expected operating environment when publishing a viscosity chart.
If the manual permits both 10W-40 and 20W-50, the lower winter grade is generally the more logical choice for consistently cooler starts. If only one grade is listed, follow that recommendation.
Which Motorcycle Oil Is Better for Hot Weather
At operating temperature, SAE 50 is a higher-viscosity grade than SAE 40. This means 20W-50 maintains a thicker viscosity range at high operating temperatures than 10W-40.
That characteristic can be useful in motorcycles specifically designed to operate with 20W-50 during sustained heat, high load, or demanding riding. However, hot outdoor weather does not automatically justify switching to a thicker oil.
Do Not Change Viscosity Based on Weather Alone
Engine clearances, oil passages, oil pump design, cooling system, RPM range, and manufacturer testing all affect the correct viscosity. Use climate to choose between manufacturer-approved grades, not to justify an unapproved grade.
A liquid-cooled motorcycle operating in a hot climate does not automatically need 20W-50. Likewise, a motorcycle using 10W-40 is not necessarily underprotected simply because the summer is hot.
Air-Cooled vs Liquid-Cooled Motorcycles
Air-Cooled Engines
Oil temperatures in an air-cooled motorcycle can be affected more directly by ambient heat, traffic speed, engine load, and airflow. Some air-cooled motorcycle manufacturers allow or recommend 20W-50 in certain conditions.
That does not mean every air-cooled engine should use it. Many air-cooled motorcycles are designed for 10W-40, 15W-50, or other grades. Cooling method is one factor, not the final selection rule.
Liquid-Cooled Engines
Liquid cooling helps regulate engine temperature more consistently, but it does not make viscosity irrelevant. Modern liquid-cooled motorcycle engines may have tightly controlled oil passages, bearing clearances, and lubrication requirements built around a particular SAE grade.
In both engine types, the manufacturer’s viscosity chart remains the deciding reference.
Can You Use 20W-50 Instead of 10W-40
Use 20W-50 instead of 10W-40 only when the motorcycle manufacturer lists 20W-50 as an approved grade for the expected temperature range and operating conditions.
Moving to a more viscous grade may affect cold-start cranking, initial oil movement, shifting feel, and how the lubrication system operates. A thicker oil may also change the sound of a worn engine, but that does not mean it has repaired the underlying problem.
Do not switch to 20W-50 simply because the weather is hot, the motorcycle has accumulated mileage, or the engine sounds louder than before. Check the manual and investigate possible mechanical problems first.
Can You Use 10W-40 Instead of 20W-50
Use 10W-40 instead of 20W-50 only when 10W-40 is included among the approved viscosity grades for the motorcycle and operating conditions.
SAE 10W-40 is not automatically too thin. It may be exactly the viscosity around which the oil pump, bearings, clearances, and cooling system were engineered. Moving to a lower high-temperature grade without manufacturer approval is not recommended.
A viscosity change should also not be treated as an easy way to gain power or improve fuel economy. Those outcomes depend on the complete engine and lubricant design, not one number on the bottle.
Is Thicker Motorcycle Oil Better for an Older Engine
Owners of older motorcycles sometimes consider thicker oil because of increased oil consumption, lower oil pressure, smoke, noise, or visible leaks. A higher-viscosity grade may change some symptoms when it is already permitted by the manufacturer, but it cannot restore worn components.
Thicker oil does not repair worn piston rings, bearings, valve seals, gaskets, clutch components, or an oil pump. Using an unapproved grade may also make cold starting and initial lubrication more difficult.
Persistent oil consumption, smoke, unusual engine noise, or low oil pressure should be diagnosed. A viscosity change may alter the symptom without correcting its cause.
JASO Rating Still Matters
Choosing between 10W-40 and 20W-50 solves only the viscosity part of the decision. It does not confirm wet clutch compatibility or complete motorcycle-specific performance.
Many four-stroke motorcycles use the same oil for the engine, transmission, and wet clutch. In those applications, the required JASO classification can be just as important as the SAE grade.
- JASO MA and MA2 are commonly associated with wet clutch applications.
- JASO MA2 represents higher clutch friction performance within the MA family.
- JASO MB is a lower-friction category and is generally not a substitute where MA or MA2 is required.
- API category should also match the motorcycle manufacturer’s requirement.
Our complete guide to JASO MA, MA2, and MB ratings explains how friction classifications relate to wet clutches and scooter applications.
How to Choose Between 10W-40 and 20W-50
Instead of relying on a general rule about weather or engine age, use a repeatable selection process.
- Open the motorcycle owner’s manual. Find the specified SAE viscosity grades.
- Review the viscosity chart. Check whether different grades are allowed across different ambient temperatures.
- Match the JASO classification. Confirm MA, MA2, MB, or another listed requirement.
- Match the API category. Do not assume the viscosity alone confirms engine performance.
- Consider normal starting temperatures. A lower winter grade may matter when the motorcycle is regularly started in cooler conditions.
- Consider sustained heat and load. Use a higher operating-temperature grade only when the manufacturer permits it.
- Do not use viscosity to hide a mechanical problem. Diagnose noise, smoke, leaks, or abnormal oil consumption.
- Check the Technical Data Sheet. Verify the product’s viscosity and performance claims before ordering or stocking it.
- Use motorcycle-specific oil when required. Passenger car oil with the same SAE grade may not have suitable clutch friction characteristics.
- Ask a qualified technician when the manual is unclear. Model-specific guidance is more reliable than a universal online recommendation.
You can review available motorcycle oil Technical Data Sheets before comparing products.
What Motorcycle Shops Should Consider When Stocking Both Grades
Repair shops, motorcycle dealers, parts counters, and powersports service locations may need both viscosities, but inventory should reflect the motorcycles they actually service.
- Do not recommend one viscosity for every motorcycle.
- Verify the model, year, engine, and manufacturer viscosity chart.
- Check JASO MA or MA2 instead of stocking by SAE grade alone.
- Keep motorcycle oil separate from similar-looking passenger car oil.
- Make Technical Data Sheets accessible to counter and service staff.
- Track local demand to avoid overstocking slow-moving grades.
- Do not promise that 20W-50 will fix engine noise or oil consumption.
Shops can compare both options through the Everest motorcycle oil range or contact Lube Squad for product and wholesale information.
The Right Oil Is the One Your Motorcycle Was Designed to Use
The main difference between 10W-40 and 20W-50 is their viscosity behavior. A 10W-40 oil meets lower-temperature winter-grade requirements and finishes in the SAE 40 operating-temperature range. A 20W-50 oil has a higher winter grade and remains within the more viscous SAE 50 range at operating temperature.
That does not make one grade universally superior. Climate, engine age, cooling method, and riding load matter only within the grades approved by the manufacturer. A thicker oil does not automatically provide better protection, and a lower-viscosity grade is not automatically too thin.
Check the owner’s manual first, then match the SAE viscosity, JASO classification, API category, and product documentation.
Technical References
The technical explanations in this guide are based on the SAE engine oil viscosity classification and the JASO standard for four-stroke motorcycle engine oils.
FAQ
Is 20W-50 better than 10W-40 for motorcycles?
Not universally. 20W-50 remains more viscous at operating temperature, while 10W-40 meets lower-temperature winter-grade requirements. The correct choice is the viscosity approved in the motorcycle owner’s manual.
Can I use 20W-50 instead of 10W-40 in summer?
Only when the motorcycle manufacturer allows 20W-50 for the expected temperature range. Hot weather alone is not enough reason to use a viscosity outside the manufacturer’s recommendations.
Is 20W-50 good for air-cooled motorcycles?
It can be suitable for some air-cooled motorcycles, but not all of them. Use the viscosity chart and specifications provided for the specific model.
Is 10W-40 too thin for hot weather?
Not necessarily. SAE 10W-40 may remain the manufacturer’s recommended grade in warm conditions. Engine design, cooling system, oil temperature, and approved viscosity range matter more than assumptions based only on outdoor temperature.
Will thicker oil reduce motorcycle engine noise?
It may change how an engine sounds, but it does not repair mechanical wear. Persistent noise should be diagnosed rather than covered up with an unapproved viscosity.
Can 10W-40 and 20W-50 motorcycle oils be mixed?
Compatible engine oils may physically mix, but mixing can alter the final viscosity and performance balance. For topping up, use the same approved product whenever possible and follow the motorcycle manufacturer’s instructions.
Do both 10W-40 and 20W-50 work with wet clutches?
Viscosity alone does not confirm wet clutch compatibility. Check the product for the JASO MA or MA2 classification required by the motorcycle manufacturer.
Need Motorcycle Oil for Your Shop or Inventory?
Lube Squad supplies 10W-40, 20W-50, and other automotive and motorcycle lubricants for shops, dealers, distributors, and service locations.