I noticed over my last two oil changes that when the oil life monitor gets down around 25% my mpg begins to decrease. From averaging 17.4 in the city to around 16.4. On the highway it drops from 21 to 18mpg. I changed my oil today (olm at 30%, I changed it because I wanted to see if mpg increased like last time) and my mpg went back up to 17.5mpg city and 22mpg highway. I use Mobile 1 5w-30 high millage oil and ac delco pf 46 filters. Yes, the oil does look dirty when it comes out. The millage is from the DIC and hand calculated. I don't think that the oil would be broken down that much considering that the OLM is set for conventional not synthetic. But, I have noticed the change over the last 2 oil changes. When I change it, it goes up instantly. Any ideas? Anyone else notice this trend?