SAE 10W-20 vs 10W-30

[nyik]

Previously, I've been using 10W-20. Yesterday, I put in 10W-30. The car actually feels better and less noise. I have an old 1995 nissan.

1 - does this mean that 10W-30 is actually better?
2 - what do all the other "numbers" mean? ie 5W-10, 0W-10, etc....

Usually, the mech puts in the oil for me, but it was running fairly low yesterday, so I decided to buy the Castrol 10W-30 from CT and pour it in myself.

Thanks!
Nelson

[manteiv]

the first number refers to the oil viscosity when the engine is cold
the second number refers to its viscosity when the engine has reached operating temperature

10W20 vs 10w30

in your case, when the engine has reached operating temperature, running the 10w30 means the oil at that temperature is more viscous than the 10w20 oil.

I am surprised you were running 10w20, did your owner's manual recommended that?

[nyik]

So, if 10w30 is more viscous than 10w20, isn't 10w20 "better" than 10w30? ie less resistence?

No, my mech told me to use 10w20.

[Pete_Coach]

So, if 10w30 is more viscous than 10w20, isn't 10w20 "better" than 10w30? ie less resistence?

No, my mech told me to use 10w20.

There used to be a time (back in the old days...yes my days), you changed the oil summer and winter. Less viscous in winter and thicker in summer. The principal was the same then as it is now. The difference was back then, you used to get 20 weight, 30 weight, 40 weight and even 50 weight oils. That was before multi grade oils were introduced.
Lighter weight oils will lubricate better initially when it is cold but will thicken with heat. Lighter weight oils will also not "cling" to oil whetted parts as much as heavier weight oils so, engines using the lighter weight oils may be a bit noisier.
Lighter weight oils were introduced in engines to save parasitic drag internally to the engine, thereby increasing power slightly but more importantly, by reducing that drag and increasing mileage and helping the corporate average fuel economy (CAFE) rating.
Bottom line, no you will not hurt the car by putting in either 10W20 or 10W30.

[nyik]

Thanks!!

[ES_Revenge]

So, if 10w30 is more viscous than 10w20, isn't 10w20 "better" than 10w30? ie less resistence?

If you go by that definition of "better" then why not pour in skim milk instead? It's less viscous than any of these

Forget about what your mechanic told you, what does the owner's manual for the vehicle say?

[manteiv]

I used to own a 1998 Altima. The manufacturer's recommendation is to use 5w30 oil all year or 10w30 and even 10w40 if you live in a hotter climate such as southern USA

Check your owner's manual for the best advice. Don't listen to anyone else.

[KorruptioN]

I didn't think I've ever seen 10W20 grade oil anywhere?

[l69norm]

I didn't think I've ever seen 10W20 grade oil anywhere?

+1, I don't remember ever seeing any consumer grade car stuff. There's 10W20 racing oil, but it's not for street cars. Also 10W20 oil for motorcycles.

[nyik]

Manual says 5W30. Went to Walmart last night after work to pick up the 4L jugs for 10.99.

I'll look for a new mech...