Antifreeze leak
 

I dont drive my truck much , just on weekends. 91000 on a 99 ranger. This is gonna sound strange ,but when weather changes from warm to cool or falls into mid 60s it leaks antifreeze and i can drive it and it wont leak. temp is fine .Truck has not leaked sense march , found antifreeze on oilpan . Truck on clean concrete under shelter. go figure.

This is odd. The only advise I have is pressure test your cooling system and your cap.