----- Original Message ----- From: feelstranger By the Book, 10W-30 is not for below about 5F and 5-30 is not for above about 15F. That's a tough overlap when temps in the morning may be -20F one week and day time highs in the 30's the next... Nat I use Mobile 1 15w50 year round in MT. On those sub 0 mornings, the car starts just fine. mike miller