For the life of me I could NOT find a min/max marker on the engine coolant reservior... This is a 2009 Prius...
The marks are very hard to see on the Gen II Prius. They are actually facing the engine. The best way to check the coolant level is to confirm that the radiator is full. Remove the splash guard over the radiator and then remove the cap. Check it when the engine and coolant is COLD. If it is full, it will look like the picture below.
