5W30 vs 5W40 Engine Oil: Which Is Better for Your Car?

Neither 5W30 nor 5W40 is universally “better”; the right choice depends on your engine design, manufacturer specifications, climate, and driving style. In most modern passenger cars, 5W30 is recommended for fuel efficiency and year-round use, while 5W40 is often preferred for hotter climates, heavier loads, or engines that run under more severe conditions.

Understanding What 5W30 and 5W40 Actually Mean

At first glance, 5W30 and 5W40 look similar, but the numbers indicate different viscosity characteristics. Viscosity is the oil’s resistance to flow and is critical for proper lubrication, cooling, and protection of engine components.

The Meaning of the Numbers

The labeling on multigrade oils like 5W30 and 5W40 follows an international standard (SAE J300), and each part of the label tells you how the oil behaves in different temperatures.

This list breaks down what each part of the oil grade number means so you can interpret “5W30” and “5W40” correctly.

• “5W” (winter rating): The “5W” indicates how the oil flows at cold temperatures. Both 5W30 and 5W40 have the same cold-start viscosity rating, meaning they will behave similarly in low temperatures at startup.
• “30” vs “40” (hot viscosity): The second number represents how thick the oil is at normal engine operating temperature (around 100°C / 212°F). A “40” oil is thicker (more viscous) when hot than a “30” oil.
• Cold start protection: Since both are 5W, they should provide comparable crankability and pumpability in cold conditions, assuming the same quality level and specification.
• High-temperature film strength: 5W40 generally maintains a thicker oil film at high temperature, which can be advantageous in high-load or high-heat situations.

In practice, this means 5W30 and 5W40 behave similarly when the engine is cold, but 5W40 remains thicker once the engine is fully warmed up, potentially offering more protection under heavy stress at the cost of slightly higher drag and reduced efficiency.

Key Differences Between 5W30 and 5W40

While both oils overlap in many use cases, their differences become meaningful when you look at temperature, engine design, and driving demands.

Viscosity at Operating Temperature

The main distinction between these oils appears once the engine is hot and the lubricant is doing most of its work under load and friction.

This list outlines how viscosity at operating temperature influences engine behavior and longevity when using 5W30 or 5W40.

• 5W30: Thinner at high temperature, which reduces internal friction, can slightly improve fuel economy, and is often favored by modern, tight-clearance engines.
• 5W40: Thicker at high temperature, offering a more robust protective film that can be beneficial for engines that run hotter, under sustained load, or are older with increased internal clearances.
• Shear stability: High-quality 5W40 oils often emphasize shear stability for high-stress use (e.g., performance driving, towing, or turbocharged engines working hard).
• Oil pressure behavior: 5W40 can maintain slightly higher oil pressure at operating temperature compared to 5W30 in many engines, which some drivers and tuners prefer for sustained high RPM use.

Because of these characteristics, 5W30 is typically aligned with efficiency and newer OEM specs, while 5W40 leans toward durability in harsher or heavier-duty conditions.

Climate and Ambient Temperature

Climate plays a decisive role in oil selection, especially in countries or regions with extreme temperatures.

The following points explain how different climates influence whether 5W30 or 5W40 will be more appropriate for your vehicle.

• Cold climates (e.g., harsh winters): Both 5W30 and 5W40 perform similarly at cold start due to the shared “5W” rating. Other factors (manufacturer spec, oil quality) will often matter more than the “30 vs 40” difference.
• Moderate climates: In temperate regions, 5W30 is usually sufficient and often preferred, as it balances protection and efficiency under everyday driving conditions.
• Hot climates (e.g., desert or tropical regions): 5W40 can be advantageous where ambient temperatures are consistently high, as its thicker hot viscosity can help maintain a stable oil film and resist thinning.
• High-load in heat (towing or mountain driving): In hot environments with frequent heavy loads or long high-speed runs, 5W40 may offer better margin against oil thinning and thermal stress.

Ultimately, both oils are designed to cope with a wide temperature range, but 5W40 tends to be favored as temperatures and engine stress increase, while 5W30 remains the default in moderate climates and everyday use.

Fuel Economy and Emissions

Modern emissions and efficiency standards have pushed many automakers to recommend lower-viscosity oils like 5W30, and even thinner grades in some markets.

This list shows how oil viscosity can influence fuel consumption and emissions, and why many manufacturers now specify 5W30 for new vehicles.

• Lower friction with 5W30: Thinner oil at operating temperature means less energy wasted overcoming internal friction, often translating into marginally better fuel economy.
• Regulatory pressure: Automakers optimize engines and oil recommendations to meet strict CO₂ and fuel economy regulations, leading to widespread factory fill and recommendation of 5W30 (or 0W20/0W30 in some cases).
• Emissions system compatibility: Some low-ash formulations of 5W30 are specifically designed to protect modern emissions systems (DPF, GPF, catalytic converters) by reducing harmful deposits.
• 5W40 trade-off: While providing potentially stronger high-temp protection, 5W40 usually introduces slightly more drag, which can marginally reduce economy compared with 5W30.

The difference in fuel consumption between 5W30 and 5W40 for a single vehicle is typically small, but across a fleet and over years of use it becomes meaningful, which is why manufacturers prioritize lower-viscosity recommendations.

Manufacturer Specifications: The Critical Factor

Whatever the theoretical benefits of 5W30 or 5W40, your first and most important reference is always your vehicle manufacturer’s specification and approval list in the owner’s manual.

Why OEM Approvals Matter More Than the Grade Alone

Engine oils are not only defined by viscosity. They also must meet performance standards issued by organizations like ACEA, API, ILSAC, and — crucially — by the automakers themselves (VW, BMW, Mercedes-Benz, Stellantis, Ford, etc.).

This list highlights why checking for the correct specifications and approvals on the bottle is as important as matching the numeric viscosity grade.

• Specific engine requirements: Turbo, direct injection, diesel particulate filters, and variable valve timing systems all impose different demands on oil detergents, ash content, and stability.
• OEM standards: Many manufacturers issue their own standards (e.g., VW 504.00/507.00, MB 229.5/229.51, BMW Longlife-04), which can be met by both 5W30 and 5W40 variants depending on formulation.
• Warranty implications: Using oil that does not meet the specified standard can, in some cases, jeopardize warranty coverage or accelerate wear, even if the viscosity seems “close enough.”
• Service intervals: Long-life or extended drain intervals often require oils with very specific additive packages and oxidation resistance, which may be available primarily in one viscosity grade for your engine.

In real-world terms, a high-quality 5W30 that fully matches your car’s OEM spec is almost always a safer choice than a random 5W40 that does not, and vice versa. The label’s approval list is as crucial as the numbers on the front.

When 5W30 Is Usually the Better Choice

For many drivers, 5W30 will be the recommended — and practically the best — option, especially in everyday conditions and in newer vehicles.

Typical Scenarios Favoring 5W30

Most modern gasoline and light-duty diesel engines are engineered around thinner oils to optimize efficiency and longevity.

The following situations outline where 5W30 is generally the more appropriate or manufacturer-recommended option for engine oil.

• Newer passenger cars: Many cars from the last decade — especially from Japanese, Korean, and American manufacturers — specify 5W30 as the primary or default grade.
• Moderate climates and mixed driving: For urban, highway, and mixed use in non-extreme temperatures, 5W30 typically offers an ideal balance of protection and fuel economy.
• Focus on fuel efficiency: If lowering fuel consumption is a priority and your manual approves 5W30, staying with it is sensible.
• Adherence to OEM servicing: If you want to follow the manufacturer’s maintenance plan and keep warranty and resale arguments straightforward, using the specified 5W30 is best.

In these contexts, 5W30 aligns with the engine’s design, allowing it to reach operating temperature quickly, circulate efficiently, and satisfy both performance and regulatory requirements.

When 5W40 May Be the Better Choice

5W40 comes into its own when engines face higher thermal loads, have looser internal clearances, or operate in climates and conditions that push oils to the upper end of their temperature range.

Typical Scenarios Favoring 5W40

Certain engines and driving styles naturally benefit from a thicker oil film at operating temperature, provided the manual permits or suggests 5W40.

This list describes situations in which 5W40 can offer advantages over 5W30 in terms of protection and stability, assuming the manufacturer allows its use.

• Hot climates: In regions with consistently high ambient temperatures, 5W40 often maintains better viscosity stability, especially under sustained highway or mountain driving.
• Performance and high-load driving: Turbocharged, high-performance, or track-driven cars may benefit from 5W40’s thicker film to protect bearings, turbochargers, and valvetrain components at elevated temperatures.
• Towing and heavy loads: Vehicles frequently pulling trailers or carrying heavy cargo can place extra thermal stress on the oil, where 5W40 is often favored.
• Older or high-mileage engines: Engines with some wear may see reduced consumption and slightly better oil pressure with 5W40, which can help minimize burning and seepage.

In these situations, the added robustness of 5W40 at operating temperature can translate into improved protection and stability, particularly where the engine regularly runs hot or under sustained stress.

Can You Switch Between 5W30 and 5W40?

Switching from 5W30 to 5W40 — or vice versa — is often possible, but it should not be done casually. It must always be consistent with the recommendations in the owner’s manual and any applicable OEM standards.

Factors to Consider Before Switching

Changing oil viscosity is a small mechanical decision with potentially large implications for engine behavior, particularly over long service intervals.

The following points set out the main questions and checks to make before deciding to change from 5W30 to 5W40 or the other way around.

• Check the manual first: Many manuals list more than one acceptable viscosity depending on temperature range (for example, 5W30 for normal use and 5W40 for hotter climates). Use those guidelines.
• Respect OEM approvals: Make sure the new oil meets or exceeds the same manufacturer specification as the previously used oil (e.g., the same VW, MB, or BMW approval code).
• Monitor consumption and behavior: After switching, watch oil level, engine noise, and starting behavior. Increased consumption or unusual sounds may signal the engine prefers the original grade.
• Avoid unnecessary experimentation: If the engine is under warranty or has no specific problems, it is generally safer to stick to the viscosity recommended by the manufacturer.

When done within the bounds of official recommendations, switching between 5W30 and 5W40 is usually safe; the key is to avoid ignoring the specifications that were used to engineer and test the engine.

Expert and Industry Trends in 2024–2025

Recent trends in engine design and regulation continue to influence which oils are favored by manufacturers and independent workshops worldwide.

What Current Practice Suggests

Technological and regulatory changes have shifted the oil landscape toward thinner viscosities, but 5W40 retains a strong role in certain segments.

This list summarizes current industry tendencies and how they shape the ongoing use of 5W30 and 5W40 in different vehicle categories.

• Shift to lower viscosities: Many new cars now use 0W20, 0W30, or 5W30 to meet fuel economy targets, making 5W30 a widely supported, mainstream choice with extensive formulations available.
• 5W40 in high-stress and European applications: 5W40 remains common in European performance cars, light commercial diesels, and vehicles operated in hotter or more demanding conditions.
• Extended drain and synthetic dominance: Fully synthetic oils, both 5W30 and 5W40, are increasingly standard for long service intervals and improved stability, reducing the relevance of semi-synthetics in newer vehicles.
• Emission control compatibility: Low-SAPS (low-ash) formulations exist in both grades to protect DPFs and catalytic systems, making it crucial to match ACEA and OEM specs, not just viscosity.

These trends mean drivers today have more high-quality options in both 5W30 and 5W40 than ever, but also more need to pay attention to exact specifications rather than simply picking a number off the shelf.

So, Which Is Better: 5W30 or 5W40?

“Better” depends on the engine, the environment, and how the car is used. For many drivers and most modern gasoline engines, 5W30 is the default best choice — because that is what the manufacturer designed around. For high-stress, hot-climate, or older engines, 5W40 can offer a useful protective margin.

Practical Decision Guide

Choosing confidently between 5W30 and 5W40 comes down to a few practical checks that apply regardless of brand or marketing claims.

This list provides a straightforward decision path to help you select 5W30 or 5W40 based on your car’s manual, your climate, and your driving conditions.

• If your manual specifies only 5W30: Use 5W30 that meets the listed API/ACEA/OEM standards. Do not switch to 5W40 unless the manufacturer provides an approved alternative chart.
• If your manual allows both 5W30 and 5W40:
  

  • Choose 5W30 for moderate climates, normal commuting, and better fuel efficiency.
  • Choose 5W40 for hot regions, frequent towing, spirited driving, or an aging engine that sees high thermal loads.

• If climate is very cold: Both 5W30 and 5W40 start similarly, but you may want to consider 0W20 or 0W30 if the manufacturer allows, as these flow even better in severe cold.
• If in doubt: Ask a reputable dealer or independent workshop to identify the correct specification and viscosity based on your exact engine code and region.

By anchoring your choice in the owner’s manual and then fine-tuning for climate and driving style, you turn the 5W30 vs 5W40 question from a guess into a reasoned, evidence-based decision.

Summary

5W30 and 5W40 are not in a simple “better or worse” relationship. Both share the same cold-start rating but differ in hot viscosity, with 5W30 favoring fuel efficiency and modern OEM specs, and 5W40 favoring thicker protection under high temperature and heavy load. The decisive factor is always your vehicle manufacturer’s recommendation and the oil’s compliance with required standards. If your manual calls for 5W30 and your use is typical in a moderate climate, stick with 5W30. If the manual permits 5W40 — especially in hot regions, for demanding driving, or for older, high-mileage engines — 5W40 can provide an extra safety margin. Matching the correct specification first, and then selecting the grade that fits your environment and driving style, is the most reliable way to protect your engine over the long term.