If you ever get an engine light saying your thermostat needs to be replaced, look to see if your coolant reservoir is cracked and leaking. 50,000 miles into my spark, the coolant reservoir was corroded to pieces where the hose that brings back the coolant connects to tank. Instead of bring back the coolant to the tank, it will leak it outside of the tank. and the car computer will tell you the thermostat is the problem.

On a Chevy Spark forum, I read that the same thing happened to someone else with my type of car. It seems like that part of the coolant reservoir is designed to corrode a lot faster than the rest of the tank. So, I'm just putting it out there that this might be something you'll run into if you own a 2015 Spark.