Mixing 5w30 with 20w50?

Not knowing what type of vehicle you have doesn't help. Gedia is correct. The climate of a country has a large bearing on the viscosity of the oil. Many, if not all new vehicles in Australia, especially fords, specify 5w30 primarily for fuel efficiency. I am not a great believer in running too thin an oil in our hot climate, but I won't go out side manufacturers specs in a new car. Some people even change the grade of their oil between winter and summer, but that may be in the case of older vehicles. I've mixed dissimilar oils in older cars for years and never had a problem. Maybe a 10w40 would be better. I ran that in a 2007 Getz[semi synthetic] and never had an issue in 93,000 klms.

If you just top off I think it s good....since the 5w30 is pretty thin. Especially if adding to used oil, or you need 10w30 or the engine has a lot of miles. I add 20w50 when I hear valve tap in my Hyundai Accent and it goes away. Plus, lot of shops like Goodyear don t have 10w30 only 5w30, I was like "you don t have 10w30, that is the

most common and that is what my car calls for."

never change the grade of oil in your car, many modern engine need that 5w oil. if your engine calls for 5w30 use 5w40 if you think it will increase oil pressure, but do not use 20w50, how low is your oil pressure, most senders are a little weak at idle, does your oil pressure change a lot from cold to hot

I have done it many times. The grade if oil often depends on what country you live in. The colder the lighter the grade if oil.

When mixed, it will avg 15W-40. That 50 is more of a racing wt oil.

There you go thinking again. Sure you can do it, it's your car. 20W50 won't help, it will harm. How do you know your pressure gauge is accurate?

you didn't mention make year engine...short answer don't do either. use the proper weight oil that meets the manufacturers spec...