I just started changing my car's oil with Motorcraft 5w-30, and want to know if it is the best oil to be using in my car? compared to valvoline and penzoil. I live in WI, so should I stick with 5w in the summer as well, or 10w?
Motorcraft oil is a good oil, whether it's the best depends. How many miles do you have on your car? A lot of people tend to switch to a high- milage or full synthetic oil above 75K miles. Not that its bad at all to use full synthetic before then, most just don't want to pay for the extra price.
As far as oil weight goes, depending on where you are in the country usually you would use 10w30 in the summer since it is a heavier oil and it does not break down as easily under heat as 5w does. And then you use 5w30 in the winter since it is a lighter oil and because it is a lighter oil it doesn't become as thick as 10w would in the extreme cold weather.
Living in Wisconsin i would definitely do the 5w in the winter but i'd say you would be safe with either 5w or 10w in the summer as it doesn't get overwhelmingly hot there in the summer.
high milage oil is made with additives that are supposed to help your old valves and seals, and it is partially synthetic so it doesnt break down as easy. You probably wont notice any difference any time soon, the only difference really is made over a long time using that stuff. It really doesnt matter whether you use 5-30 or 10-30 in the summer. In multigrade oil the first number shows what weight of oil it preforms like when it is freezing or below. The second number represents what weight it preforms like at operating temperature or when it is hot out. When you see 10W30 that actually stands for 10 Winter, 30 oil. And for any of you who are even gonna think about arguing this with me, call the corporate offices for any oil company and get the right information before you sound stupid. I learned this stuff in a United Auto Workers school so I know what I am talking about. BTW your taurus reccomends 5-30 so I would stick with that untill your engine gets much more beat up than it probably is right now. When you have a well worn engine then think about switching to higher weight oil.
As far as which oil is best. They are all pretty much the same, except for some of those cheap store brands. It just depends on your preference, I like Valvoline and I hate penzoil. Penzoil used to use high parrifin oil and I think that is an ugly shade of yellow they make their bottles. But now days they are pretty much all the same