2011 Aveo - overheating?

[motherof3]

My daughter has 2011 Aveo with approx. 27,000 miles. It quit accelerating and seemed to be overheating. She put more coolant in. Last week it did it again, we had it towed to a dealership. They tried to duplicate it overheating by driving it and did a pressure test on it - but found nothing. They replaced the thermostat - as they figured it might be that - and that was covered under the powertrain warranty (no cost to me). Today I drove it to return it to her approximately 80 miles. As I was driving I noticed that the engine temperature would fluctuate between normal and cold, then I would get either real hot or cold air from the air vents. When I reached her workplace I heard a noise like the fluid in the radiator was boiling. No warning lights came on. Any ideas? We took it to another dealership (closer to her) to have them look at it. If it's the heater core, how many hours should it take to replace it? The new dealer said it would be about 10 hours to replace it, which seems high to me. If it's the heater core, it won't be covered under the powertrain warranty, so we'll go somewhere else to get fixed, as the dealer will be priced horribly. Any info would be appreciated. Thanks.

[EAD15]

The heater core is a pain to get to in this car. The book time is 5 hours to gain access, then another 5 to reassemble. This is because the service procedure essentially calls for the entire instrument panel, radio, etc. to be removed.

[PoisonIvy]

This could be a faulty coolant resevoir cap. Do a search on this site, and you might find similar symptoms.

[ontarian_frog]

Sounds like an air bubble. When the vents go cold, it means there is no coolant in the heater core. When the heat comes back, you have coolant in the core again.

[Swift+]

Overheating/boiling indicates a bad thermostat and no heat indicates no coolat or a coolant leak, if no leak then its something else unrelated to the thermostat. I replaced my thermostat and kept getting nonfunctional thermostats. Then I bought an ACDelco and tested it before installing it by microwaving a cup of water in the microwave for 2 minutes; then placed the thermostat in the steaming cup of water, thermostat opened, pulled it out with a fork and thermostat slowly closed. Then installed the functional thermostat.

What worked for me was an ACDelco thermostat with an aluminum thermostat housing. I used the GM original thermostat housing to engine block gasket since the gasket that came with the aluminum thermostat housing is too small and caused a leak of coolant when I installed it.

[WHAT HAVE I DONE]

I had similar issue and it was simply the yellow cap on the overflow reservoir. About a $15 part and super EASY. no further issues

[2010AveoLT]

I had similar issue and it was simply the yellow cap on the overflow reservoir. About a $15 part and super EASY. no further issues

I did the same thing, but I tested the Cooling system itself a while later, and found I'm leaking from around my Water Pump.