Using the recommended viscosity is best, but a slightly thinner or thicker oil likely won't cause harm. People often wonder if using a thicker or thinner oil is safe than their engine oil manufacturer recommends. While it's best to use what's suggested in your owner's manual, inadvertently using a density one grade higher or more inferior than recommended typically poses no long-term damage. A joint inquiry is whether it's safe to use 10W-30 instead of 5W-30 oil, for instance.

Is thicker oil better for an engine?

In some circumstances, motorists have used more viscous oil in an engine. If, for example, clearances between engine components have increased or gotten sloppy, a more viscous oil can help to fill the void. Within reason, more thick oil maintains a more appropriate lubricant film between moving parts. Some have even used thicker oil in a leaky engine to prevent oil from bleeding. But really, more than thicker oil is needed for your engine. Not when "thicker" means more increased density than the manufacturer recommends. Your engine was built to precise tolerances – spaces between the moving parts. The oil ought to coat those surfaces, but it also needs to be capable of flowing into all of the tight areas in a modern engine engineered to be shorter and lighter weight and with tighter patience. So the request for a specific grade of oil is calculated. The manufacturer suggests the best quality of oil for your engine.

Let's look at two examples to illustrate.

Brad buys a new automobile that needs 0W-20 motor oil. He hangs about enough gearheads to have attended to the old axiom that "more elevated viscosity oil equals okay wear safety." Wanting the best defense possible for his new ride, he empties the 0W-20 that arrived from the factory and installs 15W-50 racing oil. Next, we have John. He's a cost-savings buff, so he buys a 1998 Toyota Corolla. It calls for 5W-30 engine oil. But he has some 10W-30 in his garage, so he uses it to alter the oil. No sense in destroying good oil. Engines are Made to Use a Certain Viscosity of Motor Oil More precise tolerances are used in constructing modern advanced engines than in earlier models. One difference is less space between the main bearings and the crankshaft journals. This is done to enable motor oils with lower viscosities, such as 0W-20 and even 0W-16, in modern engines. Since they flow more freely than lubricants with higher viscosities, lower-viscosity oils reduce internal friction and increase fuel efficiency. Automakers are turning to low-viscosity fats to help fulfill the criteria as fuel-economy demands become increasingly stringent.

Thicker Oil May Not Flow Quickly Enough

In Brad's case, his 15W-50 racing oil may need to be thick enough to flow quickly enough to fill the spaces between the crank journals and main bearings while the engine is running. His engine was explicitly designed to use a lower-viscosity oil, 0W-20. Its lower viscosity allows it to flow faster and fill the small clearances between parts, leading to a durable, consistent lubricating film. The oil won't form a constant lubricating film, allowing metal-to-metal contact and wear. Not only that, but the machine will waste energy pumping the more viscous oil, reducing fuel thrift. Since more thick oil doesn't transfer heat as well as thinner oil, working temperatures will grow, possibly leading to accelerated chemical breakdown (called "oxidation ") and toxic sludge and deposits.

Some Oil Viscosity Differences are Less Pronounced

In John's case, operating 10W-30 instead of 5W-30 produces fewer potential problems. His older engine is built with different tight tolerances than Brad's. Also, both oils have the same viscosity once the engine oil reaches operating temperature. He knows this because the two numbers in each oil's density rating (i.e. "30") are exact. It describes the oil's resistance to flow at 212°F (100°C), or standard operating temperature. However, operating 10W-30 instead of 5W-30 could make cold openings more complex. It's helpful to feel that the "W" stands for "winter." The lower the oil's "W" thickness, the more readily it will flow when cold. In this issue, 5W-30 will flow more smoothly at startup than 10W-30. Some automakers allow you to switch to a lower-viscosity oil depending on the weather.

Can heavier oil prolong a high-mileage engine's life?

Older, high-mileage engines face problems with oil stress due to age and wear and tear. In this issue, a practical method to enhance oil pressure is to use a more comprehensive oil since the thicker oils have heavier base weight oil, which can help save worn engine bearings. However, one must confirm that no knocking or strange noises are heard from the engine after changing to a thicker oil.