why is my truck leaking coolant/anti-freeze? on 2004 Chevrolet Trailblazer

my 2004 chevy trailblazer was leaking coolant so I figured since I had a big hole in the top of my resivoir that it needed to be changed so I bought a new one and got it put in but its still leaking from the same spot(the back, there is a hose in the back of the resivoir) I don't know what IS causing it. the old one was not hooked to anything so I didn't hook this one up to anything. any suggestions????? it happens all the time, it don't matter if the truck is running or not it still drips out.

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2 answers 2 comments
pressure test cooling system
Ok thanks
have your mech pressure test cooling system
Ok thanks