Hi jma5049. Welcome to the forum. There are two ways to find elusive leaks. For slow leaks, dye can be added to the coolant, then, after a few miles of driving, a black light is used to show up where the dye is coming from.
More commonly your mechanic will use a pressure tester to pressurize the cooling system up to its normal 15 pounds that it develops when the engine warms up. Leaks will be evident then as seepage or dripping onto the ground. It's a matter of searching for the source. You can develop the same pressure by starting with a full radiator, then warming up the engine. The heating and expanding coolant will build pressure that will push the coolant out of the leak.
If you're finding a really big puddle under the car, (big enough to reach both front tires), suspect a leak that is close to the bottom of the radiator or the lower hose. If you see steam when the engine is warm but not a very big puddle, that suggests the leak is up higher.
Caradiodoc
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Tuesday, June 15th, 2010 AT 7:25 PM