My dealer uses Rotella T 15w40 in all the non-synthetic-requiring cars, which I am assuming would be all the pre-98s. Mine is a 97 c230. I picked up a case of 6 gallons for $35 and some filters, so that I can have the dealer use this while the car is still under Starmark warranty. Question is, is this ok for the colder months, or should I look for something in the 5-10w range?

I will likely convert to Mobil1 5 or 10w40 after the warranty period, when I'm not paying labor for oil changes.