My 2002 sierra 1500 seems to have some vapor coming out of the exhaust. I noticed it today when looking over the truck. I have had to add coolant to it twice in the past month and was wondering why? I had someone rev it a few times and i noticed the vapor coming out the exhaust. The oil is clean and the vapor is def not smoke. It also seems to drip a little water out of the exhaust too. Anyone know if this is normal ? What could cause this? Thanks very much.