Pontiac Repair: 2002 Grand Am external coolant leak, coolant tank, coolant leak

Question
Hi Todd,
3 months ago I bought 2002 Grand Am SE 2.2L Automatic. It has 55,000 miles on it. About 3 weeks ago while driving suddenly low coolant light came on. It was nearly quarter tank left. I filled coolant and drove it three days and one morning I saw coolant leak on my drive way. It does not overheat. I called mobile mechanic to check the leak. He went under the car and checked water pump, hoses, radiator etc. He could not find the leak at all! He asked me to put Bar's stop leak and I did and again I drove for one week and last night again low coolant light came on. Once I got home I waited about 30 minutes to cool down engine and opened coolant tank cap,I heard pressure release and  saw coolant leaking middle of under the car. Leaked about one minute and stopped. Coolant tank had still half tank full.I do not know exactly where it is coming from because it was little dark in the evening. It is not from water pump or overflow hose because I put my hand around. It is not leaking always. It is a mystery for me. Please help. Thanks Walter

Answer
Hey Walter:

It could be a lot of different things is it's on the back side of the engine by the fire wall it's gotta be the water pump or the bypass hose that run along the back side of the block. Ther are 2 Big o-rings that seal that pup up. It could also be the thermostat housing which on that back side as well. lastly it could be a head gasket leaking. I havn't see any yet on that engine but it is possible. You can get a bottle of what is called coolant dye and add it to the  coolant. It is a florecent I spelled that wrong... it's a dye that when added to the coolant will help to find the leaks a black light is used and the leak will show up much better that way. Good luck :)