I was told the lower viscosity was for a colder/winter climate. Is that true? Would it be bad to use 10w30 instaed of 5w20 (both Mobil 1)?

I changed to 5W when I used to live in Houston.

According to the specs, Mobil 1 10W30 has about the same viscosity as 5W30 at operating temperatures. (They both function like "30wt" at high temperatures.) If you really need more viscosity you would have to go to something like a 10W40, but that might void the warranty.

It's possible the 10W30 will be more stable over a long interval, and not shear down or thin out as fast as the 5W30.

Here is a link to the specs I'm talking about (this is a good forum for oil issues):

http://theoildrop.server101.com/ubb/ultima...ic;f=1;t=009433 (http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=009433)

The "W" is the base weight of the oil, so 5W is a 5 weight oil. The 30 is the effect of viscosity extenders added to the oil to stabilize the oil, causing it to act as a heavier 30 weight at higher temps. This is done by adding long chain synthetic molecules that are tightly coiled at low temps thus acting close to the base 5W oil viscosity. As temps rise, these molecules uncoil and effectively thicken the oil to prevent shearing, taking over as the 5W becomes thinner than desired.

The advantage of a lower base oil is that you get much better lubricating on cold starts (cold meaning not up to operating temps). In general, you should use the lowest weight oil that will properly lubricate the moving parts which is 5W30 weight on the LS2. Ambient temperatures are no longer a reason to switch viscosities because of multi-weight performance. It is usually a bad idea to switch weights because it changes the wear characteristics of the rings and bearings as clearances change suddenly. It's also a good reason not to follow the extended oil change intervals allowed.

Never use 10-40 oils, never! The extended viscosity range means there is less base oil and more viscosity extenders in the oil. 10W40 has been "outlawed" by GM for over a decade. It WILL void your warranty.

thanks mldavis i learn something new..... cheers :friday: