Losing coolant from the reservoir but cannot see any coolant leaking on drive. Fill reservior to MAX and within ~10miles, reservoir is drained. Refill while engine still hot and don't lose nearly as much coolant. Let sit for 3hrs, coolant down just a little, refill to MAX and drive ~10miles, reservoir drained again. This morning, filled reservoir to MAX, but left the reservoir cap off. Drove to dealer, about 45 miles, reservoir down a little, but not drained. Also, car NEVER overheated. Dealer says it's two bad/leaking heater hoses...... I don't see how it could be heater hose leaking and engine temp never goes up. If heater hose was leaking, how would it drain the reservoir starting with a cold system/engine? Do you think it is the heater hose?

My '01 Jetta had a similar problem. I could always smell coolant and the bottle was always low. I crawled under the car and there it was..a caked on mess of pink antifreeze. There is a plastic intersection 3 way valve where the coolant temp sensor resides. it has 2 bolts and a rubber o-ring. Because it is plastic, it cracks. it drips down onto areas which are really not visible from above and then sizzles and melts onto areas under the engine. The part was only about $25, took 30 min to install and my problem is now fixed. Air was getting into the system through the small crack in the valve further complicating the system operation.

It is highly probable then that it is in fact the heater hose leaking. Here is how.

If your radiator level remains full, then it won't draw coolant from the reservoir. The reservoir is also an over-flow bottle in the event the engine over heats and the coolant boils, the steam can be released into the reservoir...which is obviously not happening so we don't have to consider an engine gasket leak.

The only other places that you can lose coolant from then in your situation that would be rather obscure is the heater hoses. They are in the flow path of coolant after flow through of the engine. Thus why your engine is not over heating. If they (the hoses) are leaking then the coolant return amount to the radiator will get low enough to create a siphoning of coolant from the reservoir that you have to continue to keep filling.

No I think you have a crack in the head or block of the engine, or a leaking gasket which is causing the coolant to be drawn into crankcase or combustion chamber. Pull your oil filler cap off and see if it has a foamy coating underneath or take a sniff at the exhaust and see if you detect the odor of ant-freeze.