Here is my basic understanding. Choose the first number based on your cold starting temps. If its regularly around 100 degrees where you live 5 or 10 would be fine. Choose the second number based on your operating conditions. Ideally you would analyze oil temp and pressure to choose your weight, but since we aren't doing that guesetimate your conditions. 100 degrees stop and go traffic I would definitely be using a 30 weight and probably a 40.
For example my BRZ is specced to 0w20 but I run 5w30 with an oil cooler. It only sees summer apirited and track use. 60,000 hard miles no issues.
What are your climate conditions? You could also use different specs summer/winter
Thanks for that, I live in a very temperate climate luckily. The coldest we would see in winter is 6C/ 43F and summer doesn't go above 32C/90F, 80% of the year it sits right in the middle.
So would you think 5W-30? or even a 5W-20?