I noticed that my car ran hot. Upon inspection I found I had no coolant. I let the car cool off and put coolant in. It started leaking from underneath the engine near the passenger front tire side, around where the muffler goes into the engine. This is when the resevoir cap is off, when the cap is on and pressure builds it stops when the car is off. When I turn the car on though it leaks from the same area again. Any suggestions on what this could be?