Hello, Trying to get a grasp on the cooling system in my 2004 saab 9-3. The radiator doesnt have a cap. Like most euro cars, the expansion bottle is capped, and can hold pressure. Mine has one connection going to/from the firewall, one going to the engine itself, and one going to the radiator. The one to the radiator Im sure is for filling. The one to the engine block I assume is part of the flow path, but Im not sure why. THe funny thing is that the hose going from the firewall to the reservoir is large in diameter - probably a 1" OD hose. The one going to the engine and the one going to the radiator are maybe 1/2" OD hoses. OK, so maybe that makes sense... but I did not think that typically you had flow through the reservoir, even if pressurized. Am I wrong? I give my saab as an example, but this could be a BMW, or MB vehicle too, all of which have similar systems. Can I assume that the reservoir is part of the flow path? I never see coolant flowing... If it is, then it sure is a nice way to renew maybe 1/4 gal of coolant each time youre under the hood... that has to be a good thing! Thanks!