I have a 2004 Grand Am that I was driving once a few months ago and it overheated. I immediately pulled over and shut it off. I got out and looked under the hood but there was no steam and no apparent leaks. After a while I started it up and it was normal temp. I drove it home and the next day had it towed into a shop.
They said I needed a new thermostat and water pump. Reasonable. So I got it back and it was fine for a while but then started overheating after about 10 minutes driving. But a lot of the time, it would cool off after only a few seconds. This went on for a bit and I took it back to the shop. They topped off the coolant and told me the heater core needed to be flushed, but that they didn’t do that.
So after another couple of weeks of this I called around and found a shop to take it to. They said “Oh no, that is not why it is overheating, bring it in for a second opinion.” So I took it in and they did a full flush and refill of coolant.
SAME THING. Also - the heat blows ice cold if I am idling or running at low RPMs. Also it takes at LEAST 20 minutes of driving for it to even try to blow warm air. I am getting really tired of paying mechanics to not fix this! Over $1000.00 so far!
EDIT TO ADD: Full disclosure. A few months ago the security system started to fail so I had the computer core replaced with an exact duplicate that had been code altered to remove the security check. I had to do this because it would randomly decide not to start because it thought I was trying to steal it. I had to do the reset dance with the keys every time I wanted to drive somewhere which took 10 minutes of sitting there looking like a moron in the car.