Recently, a Tik Tokker posted some "basics about engine oils." While he correctly identified that the letter "W" does not apply to Malaysian weather, he erroneously called it the oil's "boiling point." Sure, mistakes happen and they can be ignored, but it becomes a problem when thousands of people get the wrong information and trust it.
So, okay let us enlighten more on this subject.
How did the "W" start?
It all began in countries with winter. You know, when it is near Christmas (for the Northern Hemisphere) and everything becomes snow covered and water turns to ice.
Imagine you are a vehicle owner staying in such a region (say, Wisconsin). You need to switch between two grades of oil: A more viscous (thicker) oil during the hot summer months (such as SAE 40), then replace it with less viscous (thinner) oil in winter (such as SAE 10).
Oil becomes thinner when it heats up, right? So, the thicker oil will maintain a thick enough viscosity in summer and continue to protect the engine. However, this oil will become even thicker and eventually freeze over during winter.
On the other hand, a lighter oil warms up quickly and is easier to circulate during the winter months, meaning the engine is easier to start and get protected quickly. However, the viscosity becomes way too thin when the engine reaches its operating temperature.
So what did engineering do?
In the 70's oil engineers managed to combine the two attributes into a single oil i.e. thick enough for hot weather use, and remain thin enough during winter. This oil is hence called "multigrade." Whereas the old "straight grade" oils were described as SAE 10, SAE 40 and so forth, it became SAE 10W-40 and so on.
As such, the engine can start easier during winter and continues to protect the engine and its parts when it gets to operating temperature.
So the "W" means "winter"?
Yes, the "W" means "Winter." It means what is the oil's winter grade, when everything is frozen over into a winter wonderland. And no, it is not the oil's boiling point.
As such, the "W" rating DOES NOT apply to Malaysia, as the coldest temperature here is 15 degrees Celsius (unless you can ride your bike up to the summit of Gunung Kinabalu). Yes, there are those who said that a smaller number will allow the oil to circulate faster during cold starts but that is not the case, because the "W" rating is attained when tested at 0 degree Celsius.
But why are oils with "W" rating still sold in Malaysia? Because these oils are also sold in other countries around the world, including in countries with winter seasons.
But, but doesn't thinner oil freeze faster?
In truth that is what happens to fluids. A thinner fluid freezes faster than one that is thicker. However, one must remember that engine oils contain additives that counter that effect. In any case, a thinner winter grade such as 5W, although it becomes thicker quicker, will turn fluid much quicker, compared to 10W.