What type oil should I use in this? It can range from -20 degrees Celsius to +30 where i live. It is a 1986 sorry.....cant remove header from top of page

 

I had a 1989 350. I just used Amsoil 0w-40 Full synthetic that oil is good on the coldest winter morning starts and the hottest running days of the summer.

The lower the first number the better for cold starts and the higher the second number the better for warmed up operational temperatures.

0w-40 only comes in snythetic, for conventional oil I would use 5w-30 or 5w-40.