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 powertrain warranty following an internal engine failure. GM states that dexos 1 improvements from GF-4 include: engine cleanliness, corrosion protection, sludge control, wear protection, aeration control, and fuel economy. Specifications don't require the oil to be synthetic, but I don't see anything other than a blend that meets the mark. That tells us it's going to be more expensive. Here's a site to view all the dexos 1 and 2 oils in production: Your truck's preferred oil viscosity is 5W-30 -- or 0W-30 below 20 degrees Fahrenheit.

