No drops? Watch exhaust for white smoke, like starting on cold mornings. Check under carpets at floorboards at dash. Are you only filling when cold to MAX mark on reservoir. Can you see any white crusty on hose connections in engine compartment. Back compartment left rear are heating and A/C lines, do you see fluid in there. Pressure test system with dye and watch for leaks. NAPA or any major parts store will have the dye, just need a black light.