I think these cars also were not properly burped from the factory, I noticed mine was bone dry in the first few thousand miles. After refilling once or twice, my coolant level has remained pretty even since. Here is a thread about our coolant disappearing, I havent really gone through it though since once my coolant has leveled off I never bothered to go back and read more.
http://www.ft86club.com/forums/showthread.php?t=36150
Also when you brought your car in for an oil change, dont be surprised if they didnt notice your coolant reservoir was empty or top it off. Lube techs are generally not properly trained (this is by a person by person basis since some actually do take their job seriously like anywhere else), so they do not do many of the checks. They just do the oil change and get it out.