When there's no obvious external leak, the most likely suspect is a leaking cylinder head gasket. You can verify that by adding a small bottle of dark purple dye to the coolant, then checking a day later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If the head gasket is leaking, you'll find the dye inside the tail pipe.
Auto parts stores will have the dye, and those that rent or borrow tools will have the black light.
Wednesday, July 1st, 2015 AT 1:23 AM