A little A/C with a little heat mixed in & directed at the windshield should eliminate the fog quite rapidly (it starts clearing almost instantly on my car). The size of the engine is a none-issue. Otherwise, all of us would be complaining about this!
You must have cold A/C? Otherwise, you would be upset about that. If you crank up your heat full blast only, does your car throw off a good amount heat? It would be easy to overlook a bad heater core living in a southern climate. A bad heater core has been an issue with some of the older models. Daox replaced his heater core. Top_Fuel has shared some good information on this topic, too.
A mix of heat & A/C is what does it for me. My manual heat dial right in the middle is about the best when dealing with a fogged up window during the summer months.
Ill try it on 75 next time. Thank you! Ill test out the heater too.
I'm with the guys suggesting adding heat to the defog in a summer storm. I've noticed that if the defog is too cold the fog will actually be forming on the outside of the windshield instead of the inside.
View my fuel log 2015 Mirage ES 1.2 automatic: 40.4 mpg (US) ... 17.2 km/L ... 5.8 L/100 km ... 48.5 mpg (Imp)