Yeah, I live in Mesa, AZ, so I'm familiar with the heat. I tried putting one of those 'store-brand' T-Stats once, they are JUNK! You'll definately have to take a trip over to Berge Ford in Mesa or Five-Star in Scotts. and get a Motorcraft one. When I filled, I ran the heater on 'full-blast', with the car still jacked up, considering air bubbles tend to go upwards outta the system, for like 20 mins. with a big funnel I screwed into the cross-over tube. Oh, and leave the over-flow cap off until the tank fills up, filling from the cross-over tube. I use a 50/50 mix of Prestone brand coolant, and I've never gotten above the halfway mark on my temp. gauge with the A/C on auto. at 65 deg. during the AZ summertime. Well, hope that helps and good luck!