Yesterday I left the coolant reservoir cap loose after checking the fluid level. This morning (unknowingly) I drove the car and ran my heater... After about 15 minutes I noticed the smell of coolant and steam shooting out from my hood from the passenger side (where the coolant reservoir is located). I also observed the car was beginning to overheat. So I pulled over and popped the hood to find coolant and steam shooting out as well as the loose cap. I tightened the cap and proceeded to drive to a gas station to get some coolant because of all the coolant I lost. Even after pouring a gallon of coolant in the temperature guage continued to read hot (sometimes in the red, sometimes not) and fluctuate. I took it to the dealership who was backed up for hours, but a tech told me that it could be an air pocket? Is there anyone who can diagnose this situation? Any suggestions about what could havve caused this? All I did was leave the coolant reservoir cap loosened! Thanks for any help in advance...