Oil

[paul19]

My car uses SAE 5W-30 oil, what do those numbers mean, and if i were to put different kinds of oil in my car would it be really bad?

[public]

For a novice I would just say. The numbers relate to thickness. Oils with multiple numbers are "multiweights". Higher numbers are thicker. If you used a different oil, say a 10w-40 or 20w-50 you most likely would not notice a difference. It is best to use what is recommended for a regular use vehicle. Hope this helps.

[MagicRat]

Originally Posted by public

For a novice I would just say. The numbers relate to thickness. Oils with multiple numbers are "multiweights". Higher numbers are thicker. If you used a different oil, say a 10w-40 or 20w-50 you most likely would not notice a difference. It is best to use what is recommended for a regular use vehicle. Hope this helps.

To expand on this explaination, SAE just means Society of Automotive Engineers, which is just the governing body that developed the standardised testing process for measuring viscosity (thickness)

The first number is the measure of thickness when cold. The number is just on an arbitrary scale, it doesn't mean anything, it just shows that 5 is thinner than 10.

The second number is the viscosity when hot. Any oil with 2 numbers is a multigrade, (hence the letter W which stands for 'winter')that is it has "viscosity index improvers" which slow down the rate at which the oil thins out when heated.

Generally, you want a thinner oil upon initial start up so it cam pump and reach the moving parts more quickly. You want a thicker oil when hot to provide maximum protection.
Also, in cold weather, you want a thinner oil. 5W30 or 5W20 is best for winter, but 10W30 or 10W40 is better for summer.

You can put different weights of oil in your car, but you should anticipate the temperature in which your car will operate and plan accordingly, or you will shorten the engine life.

[SaabJohan]

The actual viscosity is measured in a unit called centistoke. Then there are tables how to translate them into the SAE number.

It's important to know that different scales are used so than one doesn't think that the oil is thicker when cold as the number indicates, it's just that different scales are used for the W viscosity. This is also the case with gear oil, it's rating is much higher even if the oil have the same viscosity as a motor oil, this is because they shoudn't get mixed up.

You should always use what the manufacturers recommends, if the manufacturer says 0W30, use that, don't fill it up with 20W50, don't use the thicker oil even if you have problems with high oil temperature, buy a oil cooler instead to solve that problem. When the car gets older you can use a thicker oil, this since the wear increases the clearences in bearings and so on and it will then need the thicker oil. A thicker oil also increase friction and fuel consumption.

The manufacturers also have certian recommendations on quality, these must be fulfilled also.

Today oils have become so good, at least synthetics, so that even a "straight" oil can be classified as a multigrade oil.

[paul19]

ok that makes sense. All my friends cars and my parents car use 5W-30
Is that normal since we all live in the same area and its the same temperature? Or do all of our cars recommend to use this oil.

[public]

Almost every car I see anymore says use 5w-30. Use a good oil. Synthetics are best but not required, I have a 89 Chevy with 300,000 miles on it and all on dino oil. The engine still does not burn any oil and the rings are original. I guess with synthetic oil it would last to 600,000. I don't think the rest of the car would do so well, it's looking pretty rough nowadays

[SaabJohan]

Originally Posted by paul19

ok that makes sense. All my friends cars and my parents car use 5W-30
Is that normal since we all live in the same area and its the same temperature? Or do all of our cars recommend to use this oil.

It has to do with that the manufacturers recommend it. The oil viscosity hasn't that much to do with the outside temperature, well if you live where it's cold you have to use an oil with a low winter grade but that's almost all. The oil temperature of the running engine is around 100 deg C, if it's above 110 deg C constantly power will drop, and if it's too low it will be contaminated by for example water.

The reason why the oil today is thinner is mainly because it gives lower friction losses and thereby a lower fuel consumption. To use this low viscosity oil the bearing clearences are smaller.
The manufacturers usually also recommends synthetic oils and high quality classes, the synthetics have much to do with the increased oil change intervals which are as high as 30,000 km (18750 miles) today. The oil temperature also get very high after a shutdown, so it's extra important for turbocharged engines to use a good oil.

Much of the oil used in modern cars today are 0W30 or 0W40 and in some cases also 0W20. In racing, like qualification and dragracing oils as thin as SAE 5 are used.