Question: I recently purchased a new 2011 Colorado 4x4 pickup,
and I'm not sure what type of oil to use. After researching
several websites, I found references to GF-4, GF-5, API CODE SM,
and SN. All this seems confusing, and now GM has its own type of
oil. Just what kind of oil and specs is recommended for this
truck?  Answer: SM and GF-4 are similar oil quality ratings
published by two different organizations -- American Petroleum
Institute (API) and International Lubricants Standardization and
Approval Committee (ILSAC), respectively. Both SM and GF-4 have
identified oil formulas approved by most manufacturers since
2005. But now we're converting to SN and GF-5, which are
replacing the previous standard oil ratings. In your case, GM
took it a step further by producing its own oil standard, going
by the term "dexos 1" (dexos 2 for diesel engines). Beginning
with the 2011 model year, General Motors is requiring that oils
meeting the dexos 1 standard be used in its gas-powered engines,
or risk a void powertra