Like to understand oil numbers

[kool-aide]

Hello,
I know there is a ton of good oil knowledge here. I have added a Mazda 2 to my family of cars. This is the first car I have owned that calls for a 0w - 20 oil. Lucky me my local stores only carry two brands in this. I was curious about what the numbers mean and what really difference there is, say between a 0w - 20 and a 5w - 20? I see way more 5w - 20s on the self than the lonely 0w - 20. I just thought I would ask for a little oil 101.



thanks

kool-aide

[kool-aide]

I bumbed into this.

Motor Oil Viscosity Grades Explained in Layman's Terms

I am still reading the full article, but does anyone disagree with the content?

[kool-aide]

ok. so i am sure millions have asked this before me. if you live in a climate that will normally not dip below an air temp of less than 20 degrees F. Why would you use a 0w, or even a 5w, oil? I would have to look up in the farmers almanac, but for as long as i have lived in my area. I don't recall sub 20 degrees F air temp. So if the W is for the viscocity of the oil at cold temperature, and that colder temp is defined by the nW number, say 0w or 5w. Why would an engine require a 0w oil vs. a 5w or 10w in a climate not likely to see such sub 0 temps? The only reason I ask is because of rotating oil sales and the lack of 0w 20 on the self. I realize an auto manufacture doesn't produce a car manual for each state of region of the country. once upon a time the manual had more than one recomendation based on your general local temperatures. Well...i just thought I would ask. I was lucky today and the Mobile 1 0w-20 was on sale, but it didn't stop me from thinking. Is this all just a print one owner manual literature and call it safe by the auto company?

thanks

[oldmanZ28]

Typical motor oil numbers are 0,5,10,15,20,30,40,50.
Motor oils are tested for their viscosity values at 0 F and 210 F.
A 0W-20 is equal to a 0W oil at 0 F and equal to 20W oil at 210 F.
A 5W-20 is equal to a 5W oil at 0 F and equal to 20W oil at 210 F.
At an operating temperature of 210 F,both are equal/same.
At 0 F,the 0W-20 has better pumpability than the 5W-20. Put both in a freezer and see how much better the 0 will pour out.
The 0W-20 has a higher 'viscosity index' than the 5W-20 and the higher the viscosity index,the more stable in viscosity the oil is.

Synthetic oils have a high viscosity index and are very stable,they're also more expensive.
Having worked in a oil and grease lab for 11 years,I'd like to be able to buy a 0W-50 oil because of the high viscosity index it would have,but the synthetics,with their high VI,have eliminated the need to manufacture such an oil.

[kool-aide]

That is what I thought I understood the articles information. That is why I was curious why someone would use 0w-20 in a cliemate that won't see 0 F values. If a 10w is good to at a cold temp of something like 14 F. It would seem the wider 5w - 20 store selection is perfectly fine to use, where i live. 30 bucks for a filter and syn oil seemed like a good deal, but i was lucky. looking at the 5w - 20 store selection allows me to walk i the store on almost any given day and get a great deal on oil, vs. waiting for one of only 2 0w - 20s to go on sale.

That was the root of my curiousity behind the numbers. Picking an oil that works for my climate, and determining if that oil would help broaden my buying selection.

[SteveC]

In your warmer climate (as mine) I would go with a high grade 10w-30. People who live in very cold climates use 0w oil. At startup in very cold climates you need the oil to be as thin as possible to circulate through the engine, a thicker oil will glob up.

SteveC

[kool-aide]

that was my understanding. I don't mind a 5w - 20 oil. Every brand has on on the shelf. The car does call for a W - 20. I was just unhappy the manual didn't give a cold weather range and a warm weather range. At least with a 5w - 20 i have a 100% chance of getting an oil on sale, . Likewise with a 10w - 30. I just wanted a good sounding board to make sure i wasn't nuts or misunderstanding the oils.