cochranecustoms said:
Ever since spring my MPG's have been increasing in my 98 bug, I went from 42 to 45 to 46 to 49 now. Havent changed my driving habits and driving about 50% city. My question is, I am near my 10k oil change do you think that the oil could be the factor? Just food for thought.
You'd better hope that it's not the oil. Viscosity has only a very tiny effect on fuel economy. If the oil was even partially responsible, then it would have to shear down to a 20-weight viscosity or even thinner. And realistically, the only way for this to happen would be with significant fuel contamination.
What's more likely is that your starting point, 42 mpg, was in the winter or early spring, when the fuel was still heavily winterized. And when it took longer for the engine to reach normal operating temperature. Those conditions no longer apply.
It's not unusual for TDI owners in the northern states to see their best fuel economy this time of year. Even heavy use of the AC doesn't seem to hurt fuel economy as bad as conditions in the cold months of winter.