Does a brand new car have cooling issues? The answer is NO, and this applies to all parts of the country. Does a slightly modified daily driven car with a dirty/clogged radiator and condenser have cooling issues? The answer is YES. The solution for the somewhat modified daily driven car is simple, replace your old cooling parts with new OEM ones.
Let's keep this simple; you installed this new, bigger aftermarket radiator how do you know if your cooling fan is on longer or shorter due to the added fluid? You don't unless you have a means of data logging the status of your cooling fan. In most cases, people replaced a dirty/clogged radiator with a new one. Hence the reason for the "It runs cooler with blah, blah, radiator."
Now there are a few reputable companies that make an excellent replacement radiator to a set of standards that these low budget just cannot do, and that's Ron Davis.
http://www.rondavisradiators.com/Welcome.htm
Are they expensive, hell ya and worth every penny. Call and ask for Ron Davis himself and ask him what makes his radiators so efficient. Or read the link I posted above.
Everyone's always worried about price if you can't afford the good stuff you need to save a little bit longer until you can. With proper preventive maintenance, along with certified OEM replacement parts you shouldn't have an issue. An important point to remember is this, the aftermarket DOES NOT have the means ($$$$) to do the proper R&D for daily driven vehicles. Just take a look at something as simple as a stator for a distributor. The OEM piece is far superior to the piece you get from your local parts store, eBay, etc.
FYI,
Cooling system components: Radiator, cooling fan, water pump, hoses, thermostat, antifreeze, radiator cap, reserve tank, and heater core.
I hope this helps
Michael Plummer