I just got back from a 1000 mile trip and had to put in 1 gallon of antifreeze twice on the way. The motor is a '99 Vortec 350 with ~70K on it. I've had it running in my garage for about an hour and there is no coolant leaking on the floor. No water in the oil either. There is a whitish cloud coming from the tailpipe but it doesn't really smell like antifreeze, but it smells bad. There is also a lot of liquid in the tailpipe. I'm pretty sure it's a head gasket, but is it possible it's an intake manifold gasket? Any other ideas? How do I tell which bank/cylinder is leaking if it is a head gasket? remove sparkplugs and look for ? Thanks for your help in advance!