Don't know how much you know about oil. But 30w is 30w is 30w. The viscosity or pourability is measured and is standard. All 30w oils are the same thickness at the standard temperatures.
Not saying that a different brand of oil might reduce oil usage. But it isn't because some 30w is thicker than another 30w. That just plain isn't true.

 

there is an iso range of viscosity that a 30wt falls into measured at 100*celcius. 9.3-12.49 to be exact. the two mobil 1 30w are 10, the german castrol is 12.1 and the 0w40 mobil is 14.3. in other words, 5w30 and 10w30 mobil 1 are .7 points from being a w20, while the german castrol 0w30 is .4 points from being a w40.

edit- deleted mild rant, and added more usefull info.

 

My car was fine when I got it at 50,XXX miles. It always had Valvoline 10w30 changed every 3,XXX. At 60,XXX i would use about a quart of oil every 3,XXX. My car had piston slap very badly in cold weather. At 68,XXX the oil consumption was very bad (low oil light coming on before I thought it should be low!). At high RPM's I could see smoke coming out of the exhaust terribly. At later oil changes I had a lot of metal on the drain plug. Since the car had a 75,000 GM warranty I took it to the dealer. We started an oil consumption test on the car and the service writer said GM protection plan would approve a tear down if the car used one quart in 1500 miles. I used 4 quarts in 1200 so they decided to just do the tear down right away (it was supposed to be for a 3,000 mile period!). Upon teardown the mechanic found a lot of cylinder wall taper (out of spec) and they approved a new engine. So far with 74,XXX on the car and Mobil 1 I have not had any issues!!!

P.S. Make sure your car isn't burning it through the PCV system. You can update you PCV to the 2001 and newer style to help the oil consumption. Go to www.ls1howto.com for detail on the conversion.

 

I know theres a lot of arguement to it but on my old Z28 I changed it every 3k. I figured it may or many not be necessary but the piece of mind is worth the money spent.

 

So that still means that a 30w oil is a 30 weight oil. If it was below that range then it would be a 20w oil.
And just exactly how much difference do you think that really makes in oil consumpution?
I'm pretty sure that when GM spec'ed out Mobil 1 5w-30 for the Corvette LS1 that they probably had just a little info to go on. Or maybe they just guessed that it would be OK?

 

Apparently, some.

 

They do that for fuel economy reasons. The best oil analysis' done on LS1's, LT1's, and other small block Chevy's, were all accomplished using a 40 weight oil. The sb's have always been a little "looser" by nature than most modern engines. Why they do this for fuel economy is beyond me as it makes little difference.

Jason

 

i never claimed a w30 isn't a w30. i claimed that some w30 oils were thicker than others and gave evidence to support it. and yes, it does make a difference in oil consumption as far as my car goes.