A question from the forum “Behind the Wheel” is revisited here from time to time to share practical insights.
– Is it okay to switch to a thicker oil, like 10W-40, during the hot summer instead of sticking with the recommended 0W-20?
The short answer is no, not generally. The engine’s operating temperature is not dictated by the calendar season; it tends to hover around a consistent range once the engine reaches normal running temperature. The oil passages and bearings in most modern engines are designed for the flow characteristics of low-viscosity oils. In summer heat, the oil’s job is to lubricate, cool, and seal in a very narrow path, and a heavier oil can struggle to pass through these corridors quickly enough. It might not happen every time, but the risk is real enough to warrant sticking with the manufacturer’s guidance. That is why the recommended oil weight is written as 0W-20 in many vehicles, even if it feels unusually thin like water to some observers.
Today’s engines feature tighter tolerances: smaller gaps between moving surfaces and shorter, slimmer oil channels. A fully viscous oil may not reach all the critical points fast enough, especially in engines that are relatively new or compliant with modern emission standards (typically four and newer). Because of this, manufacturers often advise using low-viscosity oils to ensure adequate lubrication across the full rev range and under varying driving conditions.
On the flip side, older engines or those with substantial wear behave differently. The clearance between crankcase components widens with age, so a high-viscosity oil can help maintain a protective oil wedge in bearings, where a thinner oil might fail to form the same robust film. If viscosity is guessed or chosen without considering wear state and engine design, there is a real danger of uneven lubrication or even engine distress that could ultimately lead to a costly overhaul.
Low-viscosity oils, while perfectly suitable for many modern engines, aren’t a universal remedy. In engines that have seen significant use or carry more wear, 0W-20 or other very low-viscosity formulations can bleed away quicker if the seals or passages are compromised, or they may not maintain adequate pressure as the oil heats up. In such cases, consulting the vehicle’s manual or a trusted technician helps ensure the oil chosen matches both the engine’s design and its current condition.
For anyone with questions about the right oil for a particular vehicle, it’s best to seek guidance from a professional technician or the manufacturer’s official recommendations. A concise check of the owner’s manual can reveal the exact weight and specification that balance lubrication, protection, and efficiency for that engine.
- The engine and drivetrain longevity benefits from adhering to simple, consistent maintenance habits that respect the recommended oil weight.
- Updates on servicing and practical maintenance tips are often shared through official channels and trusted forums, ensuring drivers stay informed about best practices.