Something that I have done in the past, which has been touched on, was sealing the radiator to the front bumper. I did this on my Mustang, but was too effective and I could not get enough heat into the radiator. I blocked off 50% of the lower grille, opened up part of the shroud, and blocked off 10% of the radiator to try and get some heat back into the engine. Making sure all the air goes through the cooler and has a place to exit is critical. If you look at a lot of race cars, they have an opening behind the radiator and duct air out the backside. This isn't easy on the Fiesta. Air needs to come in and go back out.