Wife backs her car out this morning and you notice a puddle, not large but none the less a puddle. Upon investigation you decide it is antifreeze. Has to be fixed so the dog doesn’t have it for lunch. So the search begins when she returns home. There are several methods you can use to find the leak depending upon the severity and location. The first is the tried and true searching a hot engine with the cooling system still pressurized. Of course this results in a burn or two from crowded engine compartment. You don’t find a leak. The common method it to pressurize, with a coolant tester, a cold engine, antifreeze leaks with less resistance on a cold engine than hot. Do not exceed the pressure of your cap. You can usually hear the leak if it is too small to locate. While you have the tester out check the cap as many leaks are caused by a cap that does not release pressure correctly, this can also affect the heater worse, if the cap is not holding pressure. My preferred is dye in the cooling system, after running the engine to circulate the dye use a black light to locate the source. It’s amazing how easy a leak is to trace back to its origin by using this method. If the leak is small you may have to run the vehicle or even drive it for a few days to locate the source. Check the cooling system regularly if you have to drive it as today’s cars have a low cooling system capacity. Check first for low coolant when a heating system looses efficiency or has heat at all.