Have maintained vehicle meticulously hence why I have over 150000 miles. However I'm now dealing with an issue that for now seems to be unresolvable. One day going to work, while on the highway, I noticed the engine temperature fluctuate after turning on the heat. Fearing a breakdown, I immediately got off the expressway and "limped" over to Chevy dealer.

Chevy dealer kept my vehicle for two days. Was unable to find leak in cooling system after placing dye in system. Did notice that coolant fluid was low by a gallon. They topped it off. They test drove my vehicle for 20 miles, issue "seemed" to be fixed. Yes, I had cooling system flushed/replaced at 100000 miles. Well, 2 weeks later, it was another cold morning while traveling to work, I turned the heat on and my engine temperature gauge started rising again! After work I checked the coolant level, I'm a gallon low again! I immediately purchased 50/50 Prestone Dex-Cool Extended Life Antifreeze/Coolant and topped it off again. Where is my coolant going??