Most owners of vehicles have the dilemma of choosing between 5W-30 and 10W-40 when deciding what to put in the engine oil. These two multi-grade oils are very popular globally though they do not behave in the same way at various temperatures, engine design or driving needs. It will not be 5W-30 versus 10W-40, but rather on whether it should be better or not depending on weather conditions and engine design.
Most drivers are of the opinion that when the number increases, this automatically amounts to better engine protection, independent of climatic conditions and engine designs. As a matter of fact, the wrong viscosity may cause problems: excessive viscosity in cold weather causes slow flow and extra wear during a startup, and unreasonable viscosity in hot conditions can cause that film may not be as hard as required to support heavy loads. The selection of incorrect oil grade could be detrimental either in cold start lubrication or in fuel efficiency or in high temperature protection.
To a big range of engine oil grades, covering different SAE and API standards, explore our engine oil product category to find options suited to your needs.
What Do 5W-30 and 10W-40 Mean?
The 5W-30 and 10W-40 numbers are based on 5W-30 viscosity and 10W-40 viscosity systems of classification of oils which is a measure of how the oils act within specific temperature levels.
The initial figure + W (winter) signifies cold-temperature performance – the lower the number the easier it will move in cold. The second figure depicts viscosity on high operating temperatures (approximately 100°C) of which higher figures indicate viscous oil which sustains a stronger film in high heat and load.
In practice 5W-30 remains thinner in cold operation at a cold start, allowing quicker circulation and is more viscous in operation at high temperatures, permitting the 30-grade of the viscosity to provide sufficient film strength to be used in most modern speeds. 10W-40 is larger in cold operation at a cold start and still larger in viscosity in hot operation, where it is necessary to allow the viscosity the film strength offered by its high-grade.
Key Differences Between 5W-30 and 10W-40 Engine Oil
The following is a straight contrast comparison between the two grades in respect to behaviors in real world:
| Feature | 5W-30 | 10W-40 |
| Cold-start performance | Excellent | Moderate |
| High-temperature thickness | Moderate | Thicker |
| Fuel economy | Better | Lower |
| Typical engine age | Newer engines | Older / high-load engines |
5W-30 will tend to save a little fuel by internal friction in engines that are intended to use this type of oil, whereas 10W-40 will protect more and be more drag-inducing.
Cold Start Performance and Low-Temperature Behavior
When engines are cold, they wear out the most, since the oil is not yet circulating to critical parts.
The less powerful W such as 5W would imply that the oil pumps and streams are more aggressive in low temperatures thus providing lubrication almost instantly. This minimizes contact between the metal and metal during such initial crucial seconds. Comparatively, 10W-40 viscosities higher in the cold and can slow down the flow like reducing the startup wear – particularly evident below freezing.
To get more specific guidance on the grades of oil to associate with the temperature of the season, see our cold start engine oil grade guide.
High-Temperature Protection and Film Strength
Oil at operating temperature should exhibit a stable film to be sure that moving parts are separated by loaded heat and shear.
The increase in the hot viscosity of 10W-40 increases the thickness of the oil film, which may be beneficial with older engines with wider clearances, high-mileage wear or with under-the-loads like towing. It runs richer in sizzing and 5W-30, although adequate in most uses, develops a thinner coating – adequate to modern tight-tolerance engines but which may not be as tolerant in very hot climates or in constantly heavy use.
The trick is to align the grade with actual operating tasks instead of working on the assumption that thicker is better.
How Viscosity Index Influences Grade Performance
The viscosity index (VI) is the rate at which the thickness of an oil varies with temperature Raising VI of an oil results in a longer span of consistency.
In modern multi-grade oils VI improvers are used to obtain wide protection, however the difference in actual stability of two similar grade oils is possible as a result of the quality of base oil used and into additives. A high-VI 5W-30 could passably stand heat, whereas a lower- VI 10W-40 could wear out more easily when stressed.
To find out more on this technicality,check our article on engine oil viscosity index.
Climate Suitability — Choosing Based on Temperature Conditions
The grade selection has an important role on climate.
In cold or fluctuating climates (common temperatures lower than 0C), 5W-30 is superior in its flow and less start up brushes. In permanently hot climates (varying highs above 35 o C) or where the exposure to cold conditions is minimal, 10W-40 offers dependable high-temperature film strength without the penalty of cold-start being a concern.
You can have any of the two in mind when it comes to mixed or temperate zones although one should always follow the advice of the vehicle manufacturer. To gain further understanding on the seasonal influence, read about choosing 5W-30 or 10W-40 for your climate.
Which Engines Typically Use 5W-30?
Light trucks and most modern passenger vehicles as well as fuel efficient vehicles use 5W-30.
Modern engines have smaller tolerances with varying valve timing and lower-viscosity oil emissions systems. This grade is of great priority to the manufactures in their quest to perform better in cold conditions, increase fuel consumption, and lower the emissions. It is prescribed by many OEMs in North America, Europe and Asia in gasoline and a few diesel passenger cars year-round.
Which Engines Typically Use 10W-40?
Sold engines, high mileage automobiles and severely loaded automobiles tend to respond favorably to 10W-40.
It is commonly called upon in engines with looser clearances by wear, commercial vans, motorcycles, or equipment in hot regions. It assists in maintaining oil pressure, less use in worn parts and it gives supplementary cushioning when under high load operation such as towing or construction operation.
Common Misunderstandings About 5W-30 and 10W-40
- Whicker oil is better protection always — Not everywhere. Larger oil may cause additional friction and heat in tight unObsolete engines and cause more wear or less efficiency. Formulation, additives, and suitability to the design of the engine is more important than raw thickness in protection.
- 5W-30/hot weather; too thin 5W-30 oils thinner than a film for normal driving will not wear out normally in the real world. Extreme loads and high temperature may be in favor of 10W-40 only.
- 10W-40 is applicable to every engine -False. In cold weather, or more recent engine, it may result in slow starts, excessive wear and even the fact that it can cause check-engine lights because of pressure or flow problems.
Conclusion — Choose the Right Grade Based on Use, Not Assumptions
Once again, the best engine oil grade is not about choosing the strongest but fits the viscosity with your climate, the age of engines, your conditions of usage, and your manufacturer requirements: 5W-30 is very suitable to newer car drivers in colder climates, where efficiency is a consideration, whereas 10W-40 is up to the task in warmer climates and with older or overworked engines.
In changing your owner manual, first, always consult your owner manual, take into account actual temperature and usage conditions, and watch the oil condition. Such factors also make informed choices and enable taking sure protection and durability without unjustified risks.