Does anyone care to pontificate on the recent change I made from Mobil 1 to regular dino oil... My mechanic, who's an MB specialist, has been keeping an eye on my head gasket leak on my 97 E320 130k miles. When he learned that I was using Mobil 1 10w30 immediately told me to switch to regular oil. He even said to switch to 15w50, but I just went to regular 10w30.

Since I made the change to regular oil I've noticed that my gas mileage has dropped significantly. I'd guess around 50 miles per tank. Can the switch be that drastic? I just changed plugs and all filters so I can't imagine what else it could be...

Any thoughts?