0W40 vs 5W40: Which Oil Grade Boosts Performance & Fuel Economy?
0W40 and 5W40 are multigrade motor oils; the number before the “W” tells you how fluid the oil stays at –35 °C and –30 °C respectively, while the “40” means they stay thick enough at 100 °C to protect the engine.
Drivers often stare at the shelf wondering if the “thinner” 0W40 will give them better mileage or if 5W40 is the “safer” pick. Cold-start rattle versus summer heat anxiety keeps the confusion alive.
Key Differences
At start-up, 0W40 flows 15 % faster, cutting wear in sub-zero mornings. 5W40 shears slightly less under sustained load, ideal for turbocharged engines in hotter climates.
Which One Should You Choose?
Pick 0W40 for frosty regions and frequent short trips; go 5W40 if you tow or live where 40 °C summers are normal. Always follow the manual first.
Can I mix 0W40 and 5W40 in a pinch?
Yes, they’re compatible synthetic blends, but treat it as an emergency top-up and revert to a single grade at the next change.
Will 0W40 improve fuel economy?
Expect 1–2 % better economy in cold climates; gains shrink once the engine reaches full temperature.
Is 5W40 “tougher” for high-mileage cars?
Not inherently; both grades carry the same high-temp viscosity. Use high-mileage formulas with seal conditioners instead.