2002 Honda Civic Overheating Kind of

So my civic has 167,000 miles on it. I have replaced the thermostat and radiator but the mechanics are stumped. The problem is when I am driving on the highway for about an hour or longer (I live in the mountains, so this is not easy driving) and when I come back into town and get stuck at a red light, the temperature in the car starts to slowly rise. I have never let it fully overheat. When the temperature is high, I have turned on the heat and it has come out cold. I have opened the hood as the temp is high and there is nothing leaking that I can tell. It feels hot/smells hot but I can’t figure it out. The reserve tank has fluid in it, but I cannot see inside the radiator to see if there is fluid in it. This problem has been happening for about 6-7 months, so I just try not to drive it outside of town anymore. When I am driving around town, it does not seem to have an issue. Any ideas??

I believe that you have air trapped in the cooling system. Make sure that your radiator is full of coolant. Simply checking the overflow [reserve tank] is not a valid indicator of the amount of coolant in your system. FYI: You need to find another mechanic if the ones you have can’t figure out this basic problem. You may have a water pump with corroded impellers as well. A good independent mechanic should be able to correct your problem very easily.

Is the electric fan on when it overheats? If not, do they at least turn on when you turn the AC on?

Is there a bleed screw near the thermostat housing?
Open it until only coolant without bubbles comes out.

“I cannot see inside the radiator to see if there is fluid in it.”


Have you tried using a flashlight?

I’m not familiar with the 2002 Honda Civic but my 2010 Kia Forte has a horizontal tube from the radiator cap to the radiator. I can’t see inside the radiator. This is not new. My 1963 Ford Galaxies Had a small pressure tank under the radiator cap that was then connected to the radiator.

I had this same problem last year with my Honda, only had overheating issues in stop and go traffic. After replacing the thermostat and the radiator, we found that the real problem was a blown fuse on the cooling fans…really easy fix but after we dumped money into replacing the other two first. Since that fix, there have been no overheating problems for a year.

There is a bleed valve next to the thermostat housing. It looks like a bolt with a chimney on it. Loosen it until coolant starts coming out the chimney, then tighten down.

The radiator coolant should be all the way up to the cap, so if you can’t see it, you are low. Fill it first, then bleed, then fill again. Then fill the overflow tank to about half way. You may need a new cap as well.

One more thing, I have seen new radiators where the hole for the overflow tube has not been drilled. Pull the tube off the barb under the radiator cap, then remove the radiator cap and stick a piece of wire into the barb, you should be able to see it in the neck of the radiator. If not, this needs to be drilled. Without the hole, coolant gets pumped out of the radiator and cannot be replaced.

So…from looking at other discussions, could it possibly be a warped head gasket? I don’t have any symptoms of a blown head gasket, we bled the new radiator and filled it. It’s just a strange shaped tube coming from it, so it’s really hard to see inside. I had the fans checked, they come on, so it wasn’t that.

When the radiator is full, you can see the coolant in that “strange shaped tube”. If you don’t, its not full.