My truck is leaking Antifreeze. Problem is, I cannot locate the leak. I am having to watch my reservior and have to refill it about every few months. It's a very slow leak. I took the truck to a couple places check for leaks and they cannot find it. Once in a while when the truck is idling, I can smell the antifreeze but still cannot find the leak. The leak must be small enough that it may hit the block and evaporate right away.