I run 5w30 in the 318, it came out of my 87 Diplomat and is in my 65 Cuda, over 200k miles and great oil pressure.

You need a good oil pressure gauge and use it to monitor your pressure. Do not go thicker than you need for acceptable pressure, any more just wastes gas.

They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.