The SAE paper the following graph is from has been discussed in the aviation forum before. It shows the relative cylinder wall wear vs temp for straight 10W, 10w30, and straight 30. Keeping in mind that this is just cylinder wall wear, I was still surprised that 10W and 10w30 didn't perform better at low temps. But the real surprise is just how flat the wear curve is for SAE 30. Maybe the oils companies do know what they are talking about when they put something like the following in the PDS for straight grades: "Valvoline SAE 30, SAE 40, and SAE 50 offer excellent protection to gasoline engines operating under high temperature and heavy-duty service (hauling trailers, boats or RVs for sustained periods).