Wet stacking is when your car or truck has too much soot and moisture built up in the exhaust system. This can happen when you don't drive your vehicle very often or if you do a lot of short trips that don't give your car a chance to heat up and burn off the extra soot and moisture. The soot and moisture can clog up the exhaust and make it harder for the car or truck to run. To prevent wet stacking, you should try to drive your car or truck at least once a week and make sure to go on longer trips to give it a chance the get hot.