I found this on the M1 site -- Ask Mobil 1® Go Ahead, Ask Your Toughest Motor Oil-Related Question... Or just ask us something you've always wanted to know about Mobil 1. We'll sort through all the submissions and present the best questions to our panel of automotive experts. The best questions and their answers will be posted here on the site every other week. Which Mobil 1 For A '95 Saab In Wisconsin Q: My 1995 Saab (2.3L non-turbo) recommends oil weights between 5W-30 and 10W-40. The owner's manual states that 15W-40 may be used, but not in winter. My intent is to set a personal high-mileage record with this car, so I want ultimate protection. I am considering using Mobil 1 0W-40 in the winter, and in the summer a mix of one quart 15W-50, two quarts 0W-40 and one quart of 5W-30. I know that the stock answer is to follow the owner's manual, but Mobil 1 does not have a 5W-40 or 10W-40 that would give me the greatest high-temperature protection in a weight specified in the manual. Do you see any problems with my strategy, considering that engine longevity and not warranty compliance is my goal? -- Jeff Peterson, Pleasant Prairie, WI A: While there is logic to your assumptions, mixing various grades of motor oil is not a sound strategy. Although all of the Mobil 1 viscosity grades that you mention have a similar formulation, you simply cannot assign a predictable SAE viscosity number to the mix that you are suggesting. According to our information, Saab recommends 10W-30 in your car for all temperatures, so we would suggest that you use Mobil 1 with SuperSyn in that viscosity. However, since you are specifically looking to optimize both low-temperature winter protection and want maximum durability in the summer, you can use Mobil 1 0W-40 in the winter or all year round, and you will still get SAE 40 grade protection. Alternatively, you can switch to Mobil 1 15W-50 for the summer only, but if you use 15W-50 in the summer, you must switch to a lighter grade in the colder months.