Tibbiette

Hi everyone, i've searched on google on many pages about oil viscosity and oil grades. i'm kinda familiar with it but not exactly sure about something.
i know for example 5w30 means that when cold, at startups, the oil acts as a 5 weight oil but when at operating temps it acts as a 30 weight oil. the higher the number the thicker it is.

so heres some questions,

5w, 10w, 15w, 30w 40w 50w, what temperatures do these represent?
also, i know they have 15w50, 5w50 and so on. If the vehicle requires a specific grade like 5w30, when would you use anything else like 5w50? why do they make these grades if no vehicle are recommended for it from the factory?
Also, i know people here with boosted engines use 5w50 or 15w50, why? what are the benefits?

sorry for all the questions but i couldnt find answer to these ones by searching. 02.gif

tibbytib

Well, I use to work at a grease monkey (hey, no cheap shots! laugh.gif ) and if I remember correctly, the first number followed by the w is the actual weight of the oil. Additives are normally always added to oil to improve the performance of the oil. So, the second number tells you the a certain amount of additives where added to your 5w oil to make it perform like a 30 weight oil at operating temperatures.

Here you go, I found a better explanation:

Multi-grade motor oil

The temperature range the oil is exposed to in most vehicles can be wide, ranging from cold ambient temperatures in the winter before the vehicle is started up to hot operating temperatures when the vehicle is fully warmed up in hot summer weather. The difference in viscosities for any single-grade oil is too large between the extremes of temperature. To bring the difference in viscosities closer together, special polymer additives called viscosity index improvers are added to the oil. These additives make the oil a multi-grade motor oil. The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened. This slope representing the change with temperature depends on the nature and amount of the additives to the base oil.

The API/SAE designation for multi-grade oils includes two grade numbers; for example, 10W-30 designates a common multi-grade oil. The first number associated with the W is not rated at any single temperature. The "10W" means that this oil can be pumped by your engine as cold as a single-grade 10 weight oil can be pumped. "5W" can be pumped at a lower temperature than "10W". "0W" can be pumped at a lower temperature than "5W", and thins less at temperatures above 99°C (210°F). The second number, 30, means that the viscosity of this multi-grade oil at 100°C (212°F) operating temperature corresponds to the viscosity of a single-grade 30 oil at same temperature. The governing SAE standard is called SAE J300. The motor oil grade and viscosity to be used in a given vehicle is specified by the manufacturer of the vehicle.

Some new vehicles are marked to use 0W25 oil. Some ultra fuel efficient and hybrid vehicles are marked to use 0W20 oil.
[edit]

Common multi-grade oils

Some of the common multi-grade oils are:

* 0W-20
* 0W-30
* 0W-40
* 5W-20
* 5W-25
* 5W-30
* 5W-40
* 10W-30
* 10W-40
* 15W-40
* 20W-40
* 20W-50


This info can be found here;

http://en.wikipedia.org/wiki/Motor_oil


I personally like to use a 5w oil in the winter and a 10w oil in the summer. The 5w oil is a little thinner so the oil gets up in your engine quicker when its cold out, and the 10w in the summer helps protect a littel more in the summer with the heat. I normally just get 5w30 or 10w30.

This is my .02 , I'm sure others will have differing opinions. Hope this helps you out.