No it's the low or first number to concerned with when starting a cold engine. The top or last number is for when the engine is warm to prevent engine damage.

 

i ran 10w30 my trucks first winter, then 5w40 the 2nd winter. this winter [and all last summer] i ran/running 0w40 xd-3

 

Sorry bluebill. That's what I meant by the "top" number (ie. the First number.)

 

I thought I made the mistake when I changed the oil in the fall and put in 15W40. Now I was thinking I should change it again to a 5W40 for the frigid temps. But, I figure for the same anount of money as an oil change, I'll just install an oil pan heater. That will solve the problem of trying to start the 15W molasses in -20 temps. (as long as you are near an electrical outlet!

 

The key will be to keep it plugged in. If you are using it for alot of short trips and have it parked without having it plugged in you are going to have more wear on the motor when it is below operation temp. If you keep it plugged in to help with the cold starts and drive it far enough to warm it up 15-40 should be fine.

 

I run Esso 0w-40 full synthetic all year long, towing or not towing. I think more wear occurs before the oil gets there than because the oil is to thin when it got there. just my opinion though this oil thing can be almost like a religion.
Jim O