My 2005 Honda Civic EX has been overheating. I will be taking it in to a shop soon, but just wanted to see if anyone can diagnose what could be the problem.

I noticed the overheating a couple weeks ago, and after checking the Reserve tank and Radiator, I noticed they were both low. I (accidentally) overfilled the Reserve tank, and filled the Radiator. I used a 50/50 mix.

Today, around 3 weeks later, the car is overheating again, but it was perfectly fine for the past 3 weeks with 0 overheating.

Today when I opened the hood, I noticed wet spots underneath the Radiator and Overflow tank, but nothing near the Radiator cap. The Radiator needed a good 5-10 seconds of Coolant to top it back off. Here is a picture of the wet spots

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Here is where it gets weird...I opened the Overflow cap to see a dark mixture of fluid all the way at the top!! The Coolant I used is bright orange...

enter image description here

Any ideas about what could be the problem? I don't get how the Radiator was empty but the Overfill was full of this darkish mixture...

EDIT: Also, I have no idea if this is even normal or not...but if I turn the air heater to hot, but leave the strength of the air OFF, I still feel hot air coming through the vents...Never have I had that happen in other cars

1 Answer 1


The coolant you see is mixed with that was in the system. Honda uses a blue colored coolant or someone put in global green coolant.

Best way to find a leak is to fill and pressure test. Since you said it was fine for 3 weeks and there is wetness around the radiator, I would suspect the radiator or a hose is leaking slowly.

  • How can the overfill tank be full like that with the Radiator empty???? There is a good foots worth of pipe that goes down to where the actual (Min/Max) overfill tank is..Should I syphon the overfill??? I am worried that since I just filled my Radiator, it will try to fill the overfill even more and cause explosions
    – Prodnegel
    Commented Apr 26, 2017 at 2:00
  • Shouldn't all that Overfill coolant be sucked back into the Radiator???
    – Prodnegel
    Commented Apr 26, 2017 at 2:01
  • 1
    As the coolant heats, it expands and goes into the overfill. When it cools, it gets sucked back into the radiator. A. crack in the radiator might be allowing air to get sucked in and not coolant from the overfill. Usually the side tanks are the first to break on radiator since they are only plastic.
    – Chuck
    Commented Apr 26, 2017 at 2:14
  • 1
    Never check a radiator when the engine it hot because you can get seriously hurt.
    – Chuck
    Commented Apr 26, 2017 at 2:18
  • 1
    if the overfill is full, it could be the cause of the coolant seen in the first picture. The expanding fluid has to go somewhere which on the overflow, is out the cap on top. Best to just keep the radiator full with 50/50 until you can take it somewhere.
    – Chuck
    Commented Apr 26, 2017 at 2:25

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