Really? I use either 10w/40 semi syn or 15/40, I prefer 10/40 in winter so it causes less drag when starting. Either is as thick at operating temp.
OIls with a wider spread can tend to break down more through age, so in many ways a 25/40 is better in hot weather. or a 3rd gen synthetic.
I use Lucas oils because they have a decnt oil stabiliser which helps defeat cold start wear.
