Yes, improper EGR function will effect MPG.
No EGR function with reduce MPG.
Also on any engine coolant temp effects MPG, running too cool, an issue with 4cyl, will cause a decrease in MPG, it is like running with the Choke on with a carb engine.
Gasoline engines need to run with coolant between 200-220degF for best MPG and lubrication, all oil is rated at 212degF, so 30w oil is 30w at 212degF
On most Fords the center of the temp gauge is 220degF
Fords use a 192 or 195degF thermostat, to get up to 200deg ASAP, but in cold weather the 4cyl just can't generate the heat, people often put cardboard or ?? in front of the radiator in cold weather to lessen the airflow into engine compartment, this can keep engine temp higher, especially on the highway.
Last edited by RonD; 01-25-2014 at 10:56 AM.