I usually run straight SAE30 in the GTX, but I got distracted last time I changed the oil, grabbed the wrong bottles and currently it has 4 quarts of of 15w40 Castrol, and three quarts of 20w50 Valvoline.

I guess that gives me something like 17 and 1/2 W 45??

Oops

Oh well it'll get changed in the spring anyway.



If the multigrade oil is working properly, then it should act the same as straight SAE 20 at cold temps. To me that doesn't sound too bad.

What did people do before multigrade oil was popularized? They ran straight weight and started them up when needed, right?

But if this is going to be an ongoing thing, you'd probably be better served by a 10W multigrade, I would think?