2002 Dodge Durango car runs hot

My mom used to drive this car and it was running hot, we took it to a shop to get fixed and they mis diagnosed the problem, they said it was a blown head gasket, so they charged us 1800 bucks and fixed the problem (well they thought) and when we got the car back we took it out to go get something to eat, where we went was about 30 minutes away and the temperature outside was about 65-70 F and we figured it wouldnt run hot because it just got "fixed" but sure enough it did. Now my mom has a new car and I drive the durango and I want to get it fixed but no one knows what the problem is.