HELP HELP HELP, antifreeze LEAKING

[Original 4th Gen V6]

I had my freeze plugs changed a year and a half ago, and just recently I think they may have gone bad again. My heat works sometimes, and my car leaks antifreeze after about 15 or 20 minutes of driving, when the engine is cool it doesnt leak antifreeze though. i dont understand... also my temp gauge will fluctuate from like 140-220 in a matter of a few seconds and then come back down, what could be wrong? Im bringing my car in tomorrow, im supposed to be driving 300 miles in the next few days to catch a plane and I need my car... help me PLEASE Thanks ahead of time

[Rob Bell]

Find out where it's leaking from, and you've found your problem. The reason you leak antifreeze after about 15 minutes is that the car is warmed up and pressure builds up in the cooling system, forcing fluid out of the leak. Suspect hoses or the water pump first, and if not those, then maybe the heater core or the head gasket. Coolant leaks are usually pretty easy to track down if you just check things carefully. Make sure you have good lighting, too.

[FunkZ]

That high temp fluctuation is probably caused by air in the system throwing the sensor off. Do like Rob said and see if you can find a pinhole in a hose somewhere. If not, have the system pressure tested, they should be able to determine where the leak is fairly quickly.