Understanding Oil Viscosity and Weather

I've seen this question a lot? What oil should I use?

Easy answer? Use the oil the engineer recommended.

But if you want a harder answer behind the concepts of viscosity and motor oil, then you have some studying to do.

Should I go with a 0w-20?

I don't think that's wise if the engine was designed for 30 weight once it's warmed up. You can get a tiny percent better miles per gallon ignoring the engineering that went into an engine with a thinner weight, but the catch is, this wears an engine down faster. Engine wear contributes to permanent reductions in miles per gallon. So, for example taxi's, having some of the hardest use for their miles? Thinner oil is not a good way to be saving money. Sure, if you didn't care about the next guy or gal when you're done with a car, you could go thinner because it'll save you money, but only a tiny bit, because you can pass the more used engine to the next guy - this assumes you buy new...furthermore, while under warranty, if they discovered your thinner use of oils, then you could lose your warranty. In the case of a heavily used engine like a taxi, even at the number of miles that isn't a big deal for a normal consumer, you'll have already achieved a great deal more wear.

Now, if the engine was designed for that second number to be thinner like the 20 in 5w-20 or 5w-30, then there is no issue, most likely. Some companies went to the slightly thinner oils to get better miles per gallon numbers, not because there was a matching redesign of the engine. Again, bad idea to go thinner if the engine wasn't legitimately redesigned, versus it just being an “environmental decision”.

You see, oil takes more punishment to keep metal parts off each other when it's thicker. You can't replace that protection...but some new valve trains do require it or the THICKER oil of 30, once heated up, is actually damaging those components.

Using a thicker oil is far more quickly damaging.

Unlike the subject above, I have more research to do about the viscosity that's indicated with the w, as in winter. So a 5w-20 and a 5w-30 on a cold engine actually behaves the same. I am referring to an engine that's not warmed up, not just one that's freezing cold.

The portion that I need to do more research in, is if going with a lower w or winter weight for extreme cold...is it only protecting better at startup because it can flow? Is it causing more damage as the oil heats up because vehicles that are in the middle of warming up don't have the right viscosity? Whether it's harmful after initial startup but fine after a complete warm up or not, then the gain first thing in the morning would only be balanced as a help to drivers who keep their engine warmed up for longer – if however going thinner on the w or winter side of the house, has the oil behaving well into a warm up, the it'll greatly benefit those who are frequently short tripping in their car, just like me.

- by AutoBravado

On a related subject, here's an oil additive by Lucas. It's called Lucas Pure Synthetic Oil Stabilizer:

Many of these questions that came up, came up on this video, which better illustrates the colds effect on different engine oils. So take a look at a fellow YouTuber's video called "Cold Engine Noise = OIL WEIGHT".