12 hours Ago By [email protected] (Ron King)
Over the past 40-plus years, I have changed the oil in more engines than I can begin to count. If you're about to change the oil in your car yourself , consult the owner's manual that came with your car for any specific requirements before buying your oil change supplies. You'll find important information in it, such as the type, weight, and quantity of oil required by your car's engine.
The manual won't usually tell you which oil filter is required and you may not agree on the best motor oil brand it suggests, but it is a good idea to use the specified oil weight. Pennzoil specifically warns against using different oil weights — the number following the dash — in your car's engine. It's acceptable to use 0W-20 engine oil in place of 5W-20 or even 10W-20, since the number preceding the W refers to its low-temperature viscosity.
However, you should match the oil grade exactly while your car is under warranty as any deviation could be grounds for a refused claim. In the distant past, and still for some engine applications, we had single-grade engine oils like 20W, 30W, or 40W. While a 40W oil was a great choice for a lawn mower in the Southern U.
S., that was only put into service during the hottest parts of the year; it wasn't suitable for use in a snow blower in Michigan during the winter. The numbers on the container of engine oil relate to its viscosity, a measurement of how thick and sticky it is.
Higher viscosity numbers indicate thicker, stickier oils; however, all oils become more viscous in colder temperatures. The trade-off is that higher-viscosity oil provides a more durable layer between engine components, but if the oil is too thick and sticky, it can't flow to where it's needed in time to prevent engine damage before the running engine warms it up. This situation could damage the engine's bearings, one of the more serious causes of engine knocking .
Before multi-grade oils, like 0W-20 and 5W-30, we'd have to use different weight oils for various climates. If you lived in the middle of the United States, you would often use a different weight engine oil in the summer than you did in the winter months to compensate for the temperature-induced change in viscosity. Multi-grade oils are formulated so the first number, before the W (for winter), signifies its cold-temperature viscosity, and the second number, after the dash, is its viscosity at engine operating temperature.
So in cold weather, an oil rated at 0W would flow faster to where it needs to be than a 5W. We've pointed out that using the wrong grade or weight of engine oil can lead to engine damage, specifically to the engine bearings, but if you're still reading you may want to know exactly how the damage occurs. You already know that using an engine oil with a higher viscosity slows the oil flow from being where it's needed.
So, let's start from the beginning when you turn your car on after it has sat for several hours. When the engine is cold, at ambient temperature, engine oil pools in the oil pan at the bottom of most cars. Some oil remains trapped between the bearings supporting rotating engine parts, in the oil filter, and various nooks and crannies.
The oil between the bearings is the most critical for preventing engine damage. Gravity causes the trapped oil to pool at the bottom of those round surfaces, leaving the majority of the bearing surface dry. The oil's most critical job is to form a thin layer between the bearings and the rotating crankshaft and camshaft(s).
When you start your engine, the starter spins the engine which turns the oil pump, pressurizing the oil system. Until the oil pump can supply fresh oil to the bearings from the oil pan there is no protection for them, and friction and heat can degrade them quickly. This is why multi-grade engine oils are beneficial.
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