What oil weight should I use?
 

For my 331 with 10:1 compression heading into the cold season?

Thanks,
E

Depends on how the motor was built, ask the machine shop who did the work, or the company you bought it from what oil is to be used for what temperature ranges. Depends on the bearings, rings, things like that.

Mobil1
 

If you use a full synthetic like Mobil1, then 5W30 will work for almost any reasonable clearances and at almost any climate.

At the north pole you might need 0W30 or an engine warm up banket, LOL.

Rev

I'd like to add to this post. I have a 331 9.5.1 and I'm using 5w50 syn. I used 10w30 conventional for the first 500miles after buildup. Now ever since buildup I loss about 1/2 quart of oil after about 2 weeks of hard driven. (I drive like a nut) My plugs look great all 8 of them look the same, good burn. I have no leaks anywhere. Where is this oil going? Does syn oil burn different? Should I try a different wieght of oil?