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Honda Civic 2000 Overheating

I have a honda civic 2000 and recently I noticed that it overheat only after exiting a long drive on highway. The car does not overheat for my normal daily commutes (within the city).

I tried the following:

  • Checked coolant on bot radiator and overflow tank.
  • Changed the thermostat
  • No leak on the ground in the garage where I parked the car overnight
  • No noise to lead to an eventual issue with water pump
  • Radiator fan is kicking ok
  • Had a mechanic do the chemical test for the head gasket: negatif
  • Found that there is air in the cooling system:
    tried to burp the system 2 times but air is still in the coolant system. Not sure where its coming from !!?? Might be that this could be causing the overheating ?
  • Found a crack on the manifold and changed the manifold then tried to get rid of the air (burping the system): no success. The air is still not removed completely.


  • Changed the radiator cap.

What can I do next to diagnose the overheating condition that happens only after exiting long drive highway ?

p.s: I took the car to 2 different mechanic. They spent 30 minutes to find out the cause(s) and could not figure out what is wrong.



You bleed this system by the bleed screw in the thermostat housing, not by burping. You may need a new radiator cap, that can let air into the system and usually causes overheating at highway speed.

You’ve been doing great. Other possibiliities I’d suggest

  1. a worn out water pump. The impellars can and do erode over time, rendering the pump unable to pump well.
  2. a (partially) clogged and/or internally coated radiator. Flow can be tested, and “thermal mapping” can be performed with a simple infrared thermometer.
  3. collapsed internal linings in the hose that close the hose when heated up. Hoses are cheap to replace.
  4. a radiator cap.
  5. last, but not least, you might have a breached head gasket, pushing combustion gasses into the water jacket as well as heating up the coolant.

I’d start with a cylinder leakdown test.

Thanks Keith.

I did a search on the web about the bleed screw and apparently it does not exist on Honda Civic 1996 and + models. It exist on Honda Civic < 96 and honda accord.

I did change the radiator cap but with one from AutoZone. Not sure if i need to get a genuine Honda one.

Does your lower radiator hose feel soft? Many have wire support. sometimes the hose can close up on itself due to the difference in ability of radiator flow to keep up with pump demand. A good flush and new hose might be something to consider in addition to previous good thoughts. After a pressure test of course.

Thanks ‘the same mountainebike’.

  1. How to test the water pump ? remove it and check it ?
  2. where is located that hose and how to verify it ? lower and upper radiator hoses are hot when the car is warm.
  3. I did change it. I’ll update my original post.
  4. A mechanic did the chemical test to check if head gasket is leaking or blown: negatif.

The fact that I’m trying to follow is the air in the cooling system. It looks like when air is the cooling system it may cause overheating. However I’m not sure if I’m bleeding the car correctly since there is bleeding bolt. I used the no spill funnel with coolant, then run the car until the radiator fan kickin. After multiple bubbles, they dropped but they still come back.

Either I did not bleed the car correctly or air is coming from some where in the system that I could not find where: since no liquid leak on the ground and the head gasket test was negatif.


Thanks ‘Barkydog’. When do i check if the lower radiator hose is soft ? when the car is turned off or after starting it and keep it running for few minutes ?


The best way to check the water pump on your engine is by verifying that it’s producing a good fluid flow. You should be able to feel water rushing through the radiator hoses (when the engine is a full temp) or verify with the radiator cap off that the water is flowing freely. Removal of the pump for testing is unrealistic on this vehicle because it’s driven by the timing belt. Many people proactively change the water pump whenever the timing belt is done. I like to do so every 2nd timing belt change.

The radiator hoses are the roughly 2" diameter hoses coming off the top and bottom of the radiator. A collapsed inner liner is impossible to see with the hoses installed, but would adversely affect the free flow of coolant as describe din the above comment. Since your engine has been overheated more than once, it is possible that the liners have seperated. New hoses are cheap,

Regarding the headgaskets, I’d want to do a leakdown test even though the lab strip showed no chemical reaction indicating hydrocarbons. IMHO a leakdown test is more definitive, especially since the engine has been overheated already.

You do not need a genuine Honda radiator cap, the one from AutoZone will work fine. Take a look at the overflow system. The hose between the radiator and the overflow tank should be free of cracks. The hose that goes from the cap on the overflow tank down into the coolant should be secure and free of cracks also.

Thanks ‘the same mountainbike’.

Regarding the water pump, when the car is at full temp, the radiator hoses are warm and when i put my hands on them its for a quick time that does not give me an indication whether the water is flowing freely or not. I assume it’s since both hoses (high and low) are high. When I take off the radiator cap off, the coolant level stay where its. How one can check the flow of the coolant whether through the hose or radiator cap ?

I change my water pump whenever i change the timing belt. Last change done 60000 mi ago.
Yes my engine overheated more than once. One time I smelled a bad smell after i parked my overheated car in the garage. Some thing started to melt or just it got too hot and a bad odor was released. Does this indicate any thing ?

I’ll work on changing the radiator hoses. Also I’ll check with a mechanic this week-end about doing cylinder leak down test.


Thanks ‘Keith’.

I’ll likely just go ahead and change both hoses (radiator cap <-> overflow tank and the one in the overflow tank).

I noticed that when the car overheated the overflow tank has coolant in above the max tag marked line. Could it be that radiator did not suck (for some reason) that coolant back to the radiator and hence the overheating issue (less coolant in radiator) ?

That “did not suck the coolant back in” might have happened, and if so that would indicate a bad radiator cap…or a leak. A cooling, contracting fluid mass can draw air through a leak easier than drawing water from the reservoir. That leak just might be from the water jacket through a headgasket into a cylinder.

It is possible, and that most likely would be a sign of a malfunctioning radiator cap and the cause for air in the system. When cool you can the stiffness of the hose. My closest feel test would be if it feels like squeezing jello it is bad.

The only way the engine coolant can contract as it cools and not draw that coolant back into the engine is if
(1) it’s drawing air in through a leak instead, or
(2) something in the cooling system is collapsing when the system cools. That may be a hose.

The coolant cannot and will not cool without contracting. Since the system is not designed to accomodate negative pressures (relative to ambient), if it were unable to draw coolant from the reservoir and did not have a passage for air to get drawn in, something would collapse.

When the radiator doesn’t suck coolant back from the overflow tank, it is not always the radiator cap. It can be the leak in the hose between the radiator and the overflow tank, a crack at the fitting for this hose at the top of the radiator or it can be the overflow tank itself.

There are two basic designs for overflow tanks. With some, the hose from the radiator goes to the cap on the overflow tank and another hose hangs down from the overflow cap into the coolant in the tank. You can usually spot a problem with these pretty easy.

The other type has the hose from the radiator go to a molded fitting in the tank. The cap has nothing attached to it. The tube that goes down to suck out the coolant to send it back to the radiator is also molded into the tank. These are a problem because the molded tube can develop a crack and you will have trouble finding it.

A simple test, remove the tube from the radiator. Use a coolant test bulb, even one of those cheap rising ball type, stick it into the end of the hose, squeeze the bulb and release and see if it draws coolant out of the overflow tank.

A partially clogged radiator may be the culprit. A local radiator shop (most towns have them) could take a look at it for you, and maybe have a recommendation. They could also help you air bleed the cooling system too.

For my cars, I find I can get the air out simply by removing the radiator cap and idleing the engine until the thermostat is fully open. First I turn on the heat control valve in the passenger compartment. Fully “on”. I let it idle that way for 10 or 15 minutes, the fan will turn on and off several times, and all the excess air seems to be gone in 15 minutes or so starting the timer once the thermostat opens. This might not work on other cars. It depends on the cooling system design. But like I say, your local radiator shop almost certainly knows how to bleed your car.

Thanks Guys for all your responses and tips. Very much appreciated
I squeezed both upper and lower radiator hoses and did not feel like too soft… (but its subjective).

As I mentioned in my ‘updated’ original post, i did change the radiator cap but it did not solve the overheating issue.

Thanks to your helpful responses, I have now two directions to go through:
1- A possible leak in any of the 4 hoses (upper, lower, radiator cap <-> overflow tank, hose in overflow tank).

–> Since I do not see any coolant on the ground, may be a leak if any is really small but is big enough to let air in the system.

2- Go to a radiator shop to have them check if the radiator is partially clogged.

I did an extensive search on the web about how to bleed the coolant system and the easy way is through the bleeding bolt, then letting the car run (after turning the heat/ac control to heat without opening the heat blower). But my web search is that Honda Civic > 1996 do not have bleeding bolt and the way to bleed them is like described by ‘GeorgeSanJose’. I tried that way 3 times now with the help of a no spill funnel and letting the car run until the fan kicks in But the air is not completely removed. Which lead me to think that the air is recurrent and its entering in the system from some where.

I’ll verify the 2 hoses from radiator cap to overflow tank and the one inside the tank. But very likely after that I’ll just go ahead and change all the 4 hoses (Option 1). I’ll try to bleed the system after changing the hoses and report back the results.

Thank you for your help and responses