My car is a Honda Civic LX 2002, 4 cylinder. It is overheating after I've changed the thermostat, there are no cracks in the cylinder block and radiator, brand new gaskets.

  • Is the radiator blocked : does it allow sufficient coolant through?
    – Solar Mike
    Commented Nov 26, 2017 at 18:05
  • 1
    Did you use an OEM Honda thermostat? Did you ensure the system is completely bled? The D17A1 engine is a fickle beast when it comes to coolant. Having issues with my own '03 Civic LX. Commented Nov 26, 2017 at 18:13
  • Was the car already overheating before you changed the thermostat, or only after?
    – Ives
    Commented Nov 26, 2017 at 19:12
  • The radiators on the left side so park it with that side facing up, start the car, and open the radiator, then pour coolant in until you stops seeing air bubbles. When air goes into the water jackets that's not how air cooling works. Make sure to let it cool down first, you want the radiator to be cool before you open the radiator. It builds up lots of pressure. If it's an emergency use plenty of towels and turn your face away. People suggest to upgrade the radioators because when sitting idle, they'll overheat because the fan itself isn't enough to cool down the radiator in hot weather. Commented Nov 26, 2017 at 23:37
  • @GettingNifty - Actually, the radiator is in the center and the radiator cap is on the right side of the car (as with all things, in relation to where the driver sits). But yes, you want the radiator cap to be as up as you can get it when do int this. Sitting the vehicle up hill on an incline with the radiator cap at the highest point would get you the best results. Commented Nov 27, 2017 at 15:41

2 Answers 2


There are a couple reasons for overheating.

System can't build pressure, so boiling point is lower. Could be a leak, bad radiator cap, or an air pocket. Look for visible leaks, they will eave a white residue behind. If it is the cap, you will likely not have pressure in the upper hose. Coolant overflow bottle may overflow. Not sure on the best way to determine air pockets, other than process of elimination.

Temperature goes up quickly. Heat works and helps cool the engine, but will likely not be enough to keep it in the operating range.

Could be partially clogged. Temperature increases slowly, especially under higher load. Heat helps bring it back down to normal. May be cold pots on the radiator. Both input and output hoses hot.

Fans don't come on. This will lead to overheating when you are stopped, but not when moving.

Water Pump
Little/no pressure in the top coolant hose. Top radiator hose also cold. Heat does not work.

Be aware, heat not working could also be a clogged heater core, or bad heater core valve.


Be aware that some vehicles require specific "set up" to properly fill the cooling system. For example, my 2001 Passat requires that the coolant overflow tank be loosened and raised, so that the tank becomes the highest point of the system; then, a specific hose must be loosened to make sure that no air remains in that hose. I don't know if your Honda is like this, but a look at a shop manual (or speaking to someone who knows the model) might be useful.

And while this isn't an answer, I'll ask: is the water pump operating correctly? The symptoms you report could be caused by a failed pump.

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