I'm hoping I can get some help from someone with more knowledge than myself. I have a 97 Grand Cherokee with a 5.2 V8. The water pump shaft seal was bad. I had a friend visiting who was a little bored while I was at work, since he was a decent mechanic he went ahead and installed a new pump for me. He has went home and now I have a problem. When I run the truck it starts to overheat. The heater blows only cold air like as if there is no water going through the heater core. The radiator and top radiator hose gets warm. If you accelerate the rpms there are bubbles coming up in the overflow reservoir. If you shut it off and restart the engine, you will here a burbling in the heater core area and have warm air for 10 seconds or so, at this point the temp gauge will drop for a short time and start climbing again. To my knowledge he got into a minimum amount of components while installing the pump. Before I start digging into this I was wondering if anyone might know what is causing this. I hesitate to call and talk to him after he did this favor since he will feel bad that it is not working.