My car is dropping coolant. I took it to the local shop thinking it may be the water pump. All of a sudden the temp. guage shot up and emptied all the coolant. The guy filled it up, it held the fluid, drove it to the shop and let it idle for 20 minutes, took it out on the road (about 8 miles) drove it back to my house, and all of a sudden it dropped the fluid again. Repeated the same procedure as before, and it's holding the fluid again. What's wrong? I hate to take it out on the road for a drive thinking it may repeat. What should be checked? Is it the water pump, censor, or something to do with the A/C? Thanks