[Idaho Red Rocket 3]

Hey FW, Let me answer your question with what I do and how I feel about it. I have used Castrol oils in my motorcycles and cars for 41 years. Very good products. Mobil 1 has come along and I use that too. Here is how I feel about it. Motorcycles have always been running on Castrol. Cars can go with either brand. For the Boxster S I have used M-1 several times then switched to Castrol. Could not justify the extra expense and saw/heard no difference with the Castrol. Went back to M-1 just because I can buy it for half the price. I think most of todays modern synthetics are good to use. I stay with M-1 and Castrol because I have a long history of good service. With the high heat of my motorcycles and todays cars I'm more into using a 10/40 or 10/50 weight. Those 5 and zero weights make me uncomfortable. In the end you have to find your own sweet spot and decide what to use for your own reasons. Yes it is nice to hear how / why others choose and the results they get from those choices.

If I was filling the oil in your car for general purpose M-1 10w-40 would be my first choice. Change it by 5,000 miles.