What’s the Deal with 10w40 Oil?

What Does “10w40” Mean?

10w: Viscosity in cold temps—thick enough for mild winters (down to -25°C).

40: Viscosity at high temps—stays protective when the engine heats up.

It’s a balanced oil for moderate climates and conditions.

10w40 vs. Other Grades

10w30: Thinner at high temps, better for mild climates and fuel efficiency.

5w40: Thinner in extreme cold (-30°C to -40°C), similar at high temps.

10w40: Thicker than 10w30 at heat, thicker than 5w40 in cold—ideal for heavy loads or moderate cold.

When to Use 10w40

Cold climates: Winters of -10°C to -25°C.

High-load driving: Towing, hauling, or stop-and-go traffic.

Older engines: Reduces wear and leaks in high-mileage vehicles.

Check your manual—newer cars may need thinner oils like 0w20.

Choosing the Right 10w40

Synthetic: Lasts longer, performs better in extremes.

Additives: Seek detergents, anti-wear, and viscosity stabilizers.

Certifications: Look for API SP (gasoline) or CK-4 (diesel).

Key: Match your vehicle’s manual to avoid engine damage or warranty issues.

Summary

10w40 is a versatile oil for moderate cold, heavy-duty driving, and older engines. It’s thicker than 10w30 at high temps and 5w40 in cold, offering solid protection. Pick synthetic with good additives and the right certification, and always confirm with your owner’s manual.