The 10W-30 and 5W-30 has the same oil thickness level. It doesn't really matter which you use. As the number increase say 40, 50 or even 60, the thickness of the oil increases too. Remember, thicker oil provides better protector but fuel consumption & pick up will suffer a little bit.

The 10W or 5W shows the oil tolerance level against freezing. Here in Malaysia, we practically don't really bother about the front numbers as our weather is hot through out the year.

Actually the first 2 number/letter, 5w-30 or 10w-30 is not applicable for our tropical climate. These figures show how the oil actually flows under extreme low temperature. We Malaysians will just need to focus more on the last 2 digit which is 30, 40, 50 0r even 60.

I read from this website ages ago & that fellow said:-

"I can't tell you how many times I have heard someone, usually an auto mechanic, say that they wouldn't use a 5W-30 motor oil because it is, "Too thin." Then they may use a 10W-30 or SAE 30 motor oil. At engine operating temperatures these oils are the same. The only time the 5W-30 oil is "thin" is at cold start up conditions where you need it to be "thin."

The "W" affects the oil flow only during cold start & usually at -5C & below. Our temperature hardly even reach below 25C. That is why I will usually ignore the "W" label. If we're in the States or some snowy mountains, then we can emphasize on the "W" label.

http://www.upmpg.com/tech_articles/motoroil_viscosity/

This post has been edited by Thrust: May 19 2011, 07:14 PM

Not suitable for small cc engines like Kelisa, viva & kancil... Those small cc engines needs xW-30 engine oil. This is because their small engine don't really generate much power & using thicker oil like 40 & 50 will make the engine even sluggish.

40 & 50 can be used for normal engine like Wira, Waja & usually 1.3liter engine and above.

Actually it depends on individual, the thicker the oil, the more protection it gives to your engine. That is why Castrol has SAE60 grade oil for maximum protection.

Of course it can be used on Viva...

I lazy to explain already brother... Please refer here:-

http://www.worldsbestoil.ca/which-30-weight-oil.php