My 2016 Jetta had the temp/low coolant light come on about a month ago and again on Monday. Both times it took less than a pint of water to get it back into the max/min zone. I can't find any damp places in the engine compartment. I'm wondering if the thermostat isn't opening enough and making the cooling system boil off a bit, although I don't see where it spits out. I've owned the car for a year. Any suggestions?