My Wallyworld has all flavors of mobil 1!

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0W20, 5W30 SUV regular and ep, Even 0W40. All types except for 5W40 suv. The 0W20 is in the new style bottles, as is all the rest.
 
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my local wm is the same way. the 0w20 is geared towards people with hybrids. its the same as 0w30 is to 5w30. slightly thinner on start up try and tweek every last mpg out of it.
 
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The thinner-on-startup aspect will minimize engine wear at startup, a major source of total wear. Consider 0w-20 a way to cut down on total lifetime engine wear. Running wear has proven time and time again to not be a big deal. That leaves startup wear as the dominant factor.
 
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Climate determines how much of a factor startup wear really is. For example; where I live there is NO advantage of a 0w30 vs 5w40. If your climate never sees temps below 20F you would see no decrease in lifetime engine wear by running a 0wXX vs a 5wXX. In fact running a 0wXX's in a hot climate may lead to shearing and cause MORE engine wear. Bottom line... use the appropriate weight for your climate.
 
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In my opinion, most of your elevated wear is unavoidable. It's going on, at varied degrees, until the pistons are expanded 100%. This takes about 20 minutes ..or so many combustion pulses. The use of the lighter weight oil mainly reduces the energy expended during warm up. The trick they're trying to manage on a fine line is compressing the cold vs. hot visc as much as possible ..and still be adaquate @ 100C. Climate will probably alter the depth and the length of your elevated wear state ..but I doubt that it's the first 0-30 seconds of your operation.
 
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I'll partially agree with Gary on this one. Startup wear is caused by the oil being below the various vapor and sublimation points of combustion byproducts, build up of unburnt hydrocarbons which aggregate while the oil is cold and are not boiled off, acidic attack of the engine metal due to oxidation of the oil and hydrobromic acids which aren't boiled off until the engine is warmed above 140F, AND insufficient lube at start up. Of that, approximately half is due to insufficient lube at start up. A cold start can cause between 200-1000 miles of wear (normalized by the wear rate with warm engine, with clean, good oil on a flat highway at constant highway speeds). The actual wear factor depends not only on how many times you started your car, but how the temperature ramped up, and how long the total trip was (was it long enough to boil off combustion byproducts, etc.). If you don't idle much, and warm fairly quickly, the start could be as little as 100 miles of wear, but if the initial temperature was low, you idled to warm, you take a very short trip, and your oil is below average, wear can be 1000 miles/startup. If you subtract off the metal desolution rates from the non-load mechanisms you still get 100-500 miles of wear from insufficient lube at start up. So with about half the wear from insufficient lube at start up, you obviously want to select a viscosity of oil that will decrease the amount of time it takes for the engine to be lubricated "sufficently". Now here's the million dollar question. How much can you influence how quickly "the proper" lubrication is established with a viscosity change in oil? For example, if at cold start one oil has a viscosity of 700 cSt and another is 3500 cSt how much faster will "the proper" lubrication be established with the 700 cSt oil? Now factor in different engine designs, and it'll probably even more difficult to answer the question at hand with pin point accuracy. By the way, here's a picture of Gary in real life. [Big Grin]
 

Patman

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You guys have a much better M1 selection at Walmart than us. We've only got 5w30, 10w30 and 15w50 up here. You'd think that we'd get 0w20, 0w30 and 0w40 as well up here considering how a lot of areas of Canada are so cold.
 
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