you might want to go with something a little better suited for the winter months, a 5W-30 would probably be better. All automotive oils (well mostly all) are multi-grade oils meaning they meet the viscous requirements for two or more SAE (society of automotive engineers) grades. The W stands for winter and the number before the W is the viscosity of the oil at low temperatures. The number without a W is the weight at normal engine operating conditions.
So in other words, with 5W-30, at low temperatures, the oil will be thinner (noted by the smalled number 5) and at higer temperatures, the oil viscosity will be thicker so that the extra ambient heat will thin it out to where is should be.
You could also go with two different oils if the temperature change is really exsessive. In the winter months you could use a 5W-30 and in the summer, if you don't expect to see any cold temperatures and lots of extra hot days, then you could switch to a 10W-40 or 20W-50.
The last thing to take into consideration is the condition of your engine. If you suspect that your bearings and rocker shafts are worn, or if you think you have excessive blow by, then you might want to go with the heavier oil as it will help to seal up the excess clearances. However, while heavier oils give some extra protection to worn bearings and other loose engine parts, lighter oils are better for engines in good condition. Lighter oils actually reduce friction because they can flow more easily. This improves both fuel efficiency and engine life.
Hope this helps.
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