[ccjohnson]

It could possibly be as simple as a bad radiator cap. We will keep our fingers crossed here. If it is getting into the exhaust side somewhere, ie a cracked head or bad head gasket, you should be able to smell it in the exhaust. Might also be a water pump leaking at a rate slow enough when driving that it drips and gets evaporated fast enough that it doesn't accumulate enough anywhere to make a puddle when you stop. Glad to hear you are taking it to CAT to get checked out. Coolant leak is not something you want to ignore.