That pretty much says it all. 2006 S40 2.4i with 209,000 miles. The coolant leaks rapidly from some point in the engine compartment that I can't see. It drips down a seam in the transaxle case and onto the garage floor. It only leaks if I turn on the heat, and it stops when the overflow reservoir is empty. The car doesn't overheat for at least the 90 miles I tested it with empty overflow reservoir. There is no leak inside the passenger compartment, so it's not the heater core, right? My best guess is the hose leading to the heater core, but I don't know how to find that.

Is there a "flow" chart for the cooling system?

Thanks for any advice.

 

A common place cars like yours leak is this crazy looking thing they call the upper radiator hose. Can and does leak at all the t fittings. Your car does not have a low coolant warning system - I would not suggest driving it knowing it leaks. Overheat it a little too much and then you've got a very expensive problem that will be out of your repair expertise. It's very simple to find the leak at this point using a radiator pressure tester.