[mchedlishvili]

My ford fusion (2010, 110 K miles) fuel consumption increased drastically. I suspect that it is the thermostat stuck open as it takes 7-9 minutes to reach coolant temperature operating mode. Has anybody experienced similar issue?

 

[bangster]

A vehicle not running at optimum temperature will use more fuel, first because it takes longer to go to closed loop operation, and because it will dump more fuel when it is cooler.

Also at 110k miles spark plugs, if the original ones, should be replaced. worn plugs can also cause poor fuel economy.