Just like Topic says I changed my 106k mile Jeep 4.0L Cherokee. I put 10w30 MaxLife in it after running 5w30 and 10w30 standard Valvoline in it for the first 106k miles. i used 5w30 when the Jeep was newer less than 50k miles after the first 50k I switched to 10w30 in the winter and 10w40 in the summer. My main problem is I was getting 300 miles to a tankful and it was taking about 15-16 gallons to fill up about 19-20 miles to the gallon well I am now only getting about 17-18 MPG. What gives the only thing that changed was the Oil.