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My car decided to overheat yesterday. It was noticed while we were waiting to pick someone up from the airport. We shut the car off until they arrived. (15 minutes or so) We then drove home with the heat gauge not getting hot.

When we got home I let the car cool. I then added a small amount of coolant (size of a yogurt container) just to top it off. i also added a bit to the reservoir to bring it above the "low" mark.

I guess my question(s) would be:
Should I be concerned about it happening again or was the little bit of fluid I added enough to make a difference? Does the fact that the car doesn't overheat while drive mean the thermostat is not the issue? If none of the above, what would be the most likely issue that would cause this?

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    make sure the radiator fans are working
    – user4546
    May 8, 2015 at 23:16
  • The first place to start is at the fan relays. If those are good, apply power directly to your fans to verify they are working. From there, it gets ugly.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 9, 2015 at 1:39
  • What size is a yogurt container for you? Around here yogurt comes in several sizes.
    – Nate Eldredge
    May 10, 2015 at 4:26
  • I ran the car for about 15 minutes with the hot air blowing and the temp was at the normal position (under half the range) I checked the fan and it didn't kick on. I then turn the AC on and the fan still didn't kick on. for the yogurt container; a small Chobani size container. (about 5 oz)
    – Frozen1337
    May 11, 2015 at 14:07

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Should you be concerned about this happening again? Yes. You haven't diagnosed or fixed the problem, so the chances of it going away with no further effort from you are very slim.

Because the car does not overheat while driving, the thermostat is probably working just fine. The two scenarios which indicate a failed thermostat are

  • Overheating very shortly after starting the car, but no coolant leak. Heater blows hot.
  • The car does not reach operating temperature while driving, more commonly in cold weather.

As stated in the comments, the most likely cause of your problem is that the radiator fans are not kicking on. With the A/C on and the car idling, the fans should kick on regularly, and on many cars at least one fan will run full time if the A/C is on. This makes it very easy to check. The causes for a fan not kicking on can be a bad fan, a bad fan relay, or a bad temperature sensor. Some cars use different sensors for the fan and the coolant temperature information sent to the ECU, but I don't know why or if your car is one which has that type of setup. The fan and relay are easily testable, so check those first.

If your fan is kicking on as it should, you could have a partial blockage in your cooling system, a bad water pump, or worse. Start with a coolant flush and work from there.

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  • What would be the best way to go about checking the fans and the relays? could I hook up a couple of leads to a 9v battery and apply direct power? (if 9v would even work)
    – Frozen1337
    May 11, 2015 at 14:10
  • Use the car battery. A 9v battery would not release enough current to do anything meaningful even if it was outputting 12v. Make sure you've correctly identified the leads before doing hooking the battery to the fan. The relay should have 5 pins. 3 of them are for high current circuits (like a SPDT switch) and two of them make the active circuit flip when 12v is applied across them. You'll hear a click. Google can tell provide more details on checking relay functionality.
    – Lathejockey81
    May 11, 2015 at 15:20

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