Please fill out the following to ask a question. MAKE:Buick MODEL:Century YEAR:1999 MILES:Approx. 165000 ENGINE:3100 V6 DESCRIBE ISSUE....Coolant leaks but later on after sitting. Go outside and there is a big wet spot of coolant under the car. I fill up the reservoir tank, get it up to temperature and watch for leaks but there is literally none at all. Turned the heat on and off full blast here and there to have coolant going through the heater core but still nothing. It did do this a little ways back when it was cooler outside but then stopped for awhile during the summer and was unable to find the leak then because of it just not doing it anymore. It was cooler outside this morning when my girlfriend took the car so I am somewhat stumped on this one. In almost every coolant leak case I've dealt with, it has revealed itself but not this one. Any suggestions would be greatly appreciated. Thank you.