Rainy days

On rainy days my 2004 Hyundai sonata V6 acts like it doesn’t want to drive. It starts but hesitates and you have to start it again. I don?t trust it on rainy days, its fine anytime else. Could the belt be slipping? Also I have noticed that the antifreeze level is different from time to time in the reservoir on cold. Also how do I release the belt tensioner ; do I push down or up.

Belt is not likely the problem, more likely moisture getting into something electrical. You might replace the distributor cap, rotor, wires, and plugs, if that hasn’t been done in a while.