Hi, I am new to the forum, I have a 2004 Chevy Silverado 5.3 with just over 150k miles on it. Over recent months I have noticed that I slowly lose coolant over time (about a quart or so every 500 miles). There are no signs of external leakage, but every now and then I think I can smell antifreeze. I particularity seem to get a whiff of coolant after backing a trailer up hills, this at first made me think it was coming from the exhaust, but I'm not sure since there is no smoke. My biggest concern is that I cant find any coolant leaking anywhere. I did notice once a couple months that the floor was wet under the mat, however it did not smell like antifreeze and has not occurred again so I have pretty much ruled out heater core. I have read some about Castech heads having problems cracking, but there is no way to tell if I have them without taking the engine apart. Also head gasket is an obvious possibility. So my question is before I go and tear apart the engine and take the heads off to see if its head gasket or if I have the faulty Castech heads am I over looking any "simpler" problems that could be to blame? Thanks!