So I bought an HHR last week. Always loved Chevy vehicles. This is my first car newer than 1990. I filled the tank for the first time today and found that it has a slow drip of gas coming down. When I had it to 3/4 tank it did not leak so it's only in a full tank. What would cause this and how would I fix it? Have not made it under the car yet as its all snow and ice everywhere here in Maine.

 

It could be the vent tube from the filler tube to the evap canister or you just over filled the tank.
When you pump gas, stop as soon as the pump shuts off , do not try to top it up.

 

A hole in the tank?

Have to wait to crawl under it.

 

The pump didn't turn off at all. However I've had it up in the air and see no holes in the tank there is a dent at the top of the rear of the gas tank but not seeing any breaks or holes anywhere on the tank itself.

 

Coming down from where?

 

The gas pump does not shut off when the tank is full?

That means there is a hole in the filler or vent; they work on vapor pressure.

 

X2

If you over fill, the gas can run into the EVAP canister, which is not good in itself but will not give the description of your problem.
How high is this "dent" ?
Is it all the way to the top of the tank and the bottom of it is maybe 3/4 ?

 

You mean right where a crease in plastic would cause a tear?

 

Or is it leaking from the filler cap? Do you see it dripping on the ground or down the side of the car.

 

Just a bit of clarification here. Gas vapor pressure is used in a "Vapor Recovery System" only from fuel pump nozzles to underground tank. Only at fueling sites mandated by EPA for vapor recovery in non compliant emission states only.

Non vapor recovery nozzles (about 90% of what is used today) cuts off when liquid covers the small hole at the end of the nozzle.
I have been in that business for over 35 years and have seen and used all brands.