Because oil gets thinner as it heats up. Or you could say it gets thicker when it cools down. Say your engine needs weight oil when it is running at operating temperature. Well, weight oil will work perfectly well when your engine is warmed up.
But when you go to start it on a cold winter morning, that weight oil is considerably thicker and has a hard time moving when you turn the key. These products are one grade or viscosity or weight when cold and another when warm. You have seen 10W, 5W, and the like. The first number refers to the grade when cold and the second when warm. Actually, the oil itself is the lower grade and contains additives that make it resist thinning out as it gets hot, thereby making it work like a higher-viscosity oil.
So, 5W is a 5-weight oil that acts like weight when warm. When might it make sense to use straight weight oil ie. SAE30 rather than multi-weight oil 5W? Straight-weight oil has one potential advantage over its multi-weight cousins. Because it does not contain viscosity improvers the additives that allow a low-viscosity oil to perform as a higher-viscosity oil , straight-weight oil has better shear protection. Shear is the breakdown of viscosity during operation, especially when an engine is running at high RPMs.
Some muscle cars with older engines might benefit from straight-weight oil, unless they are driven in the cold, in which case the benefit of a multi-weight oil outweighs the improved shear resistance. Most engine wear occurs not when the engine is hot, but on startup when the engine is cool.
If you drive a classic, you might consider straight-weight. That said, straight-weight oil is never recommended for an engine that calls for multi-weight oil. Is thicker oil better for an engine? There are some circumstances where drivers have used thicker oil in an engine.
If, for instance, clearances between engine components have increased, gotten sloppy, a thicker oil can help to fill the void. Modern motorcycle oils have many of the same additives as car oils, Motorcyclist reports. However, because motorcycle engines spin faster and share oil with the transmission, they require different oil additives.
And for extremely cold climates, some OEMs recommend going to a lighter-viscosity oil, Amsoil reports. However, there are limits to this. Going from a 0W to a 5W would have the opposite effect: the engine would have trouble pumping it.
So theoretically, you can go from a 5W to a 0W or a 5W to a 5W Follow more updates from MotorBiscuit on our Facebook page. By: Staff Published October 5, Older vehicles. As engines age, their parts often wear each other down. As a result, there can be more space between the parts of a ,mile engine than in the engine of a brand new car. For older vehicles, consider a higher oil weight to help fill in this extra space.
Very cold temperatures. If you often take short trips and live in a very cold climate, consider a lower number. Thin oil can work through the engine quickly on a cold day, protecting its parts from the moment it starts. Overhead engines. Because the oil needs to travel to the overhead cams and valve train, most mechanics recommend a lower weight for overhead engines. Jeep Wrangler Reliability. Preparing Your Car or Truck for Towing.
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