Honda Civic (2001) Coolant Reservoir Full & Leaking

My 2001 Civic sedan coolant reservoir was full after a long drive - with coolant blown out from the top. I am trying to isolate the problem and would appreciate any helpful comments.

  1. I Did not notice if temperature gauge rose above the mid-point on the gauge.
  2. I Discovered issue after 120+ drive on a hot day (90 degrees plus).
  3. The car has almost 230,000 miles.
  4. About 1,500 miles prior to this incident I removed my drive belt and replaced it with the shorter drive belt to circumvent the A/C compressor as it or the compressor clutch crapped out on me.
  5. The morning after this occurred the coolant reservoir was still full
  6. I removed the radiator cap and ran the engine for about 15-20 minutes. During this time I noticed the coolant in the radiator begin to rise into the fill neck area of the radiator - no bubbles or movement other than up into the neck area. The top hose was warm and then got hot but it seemed the bottom hose remained cold. I then throttled the gas briefly and nothing happened to include the radiator remaining off. The temperature gauge read just below the mi-point. I then throttled up to about 3,000 RPMs and coolant blew out of the radiator – about 1/2 to 1 liter of coolant came out. At that point I shut everything down, installed the radiator cap, and cleaned up the coolant. I noticed the bottom hose appeared to now be much warmer than before the coolant blew out. The next morning the coolant reservoir was empty.
  7. Today, about one week later, I applied power at both fans and both worked. I checked the relays and both registered no continuity across terminals 1 and 2 - as they should. I checked the radiator fan switch for continuity when cold and there was NO continuity across the contacts - as it should. I ran the engine for about 20 minutes with the radiator cap installed. The temperature reading rose to just below mid-point (normal) and stayed there. Radiator fan had not come on yet. I throttled up and nothing. Idled for several minutes and the temperature gauge rose to about ¾ of way to “H.” I throttled the engine to look for smoke from the tailpipe – there was none (there is no history of any kind of smoke coming from the exhaust of my civic). I throttled up again, the temperature gauge dropped quickly below the mid-point, and the radiator fan came on for the first time. After the fan kicked off the temperature gauge again rose to ¾. I hit the gas, the temperature gauge dropped quickly to below mid-point, and then the fan came on again.

I was thinking this could be a blown head gasket but now I am questioning my initial thoughts. As of right now there is no coolant in the reservoir. One would think if the head gasket was blown that I would continue to get fluid in the reservoir even with the lost ~1 liter from my earlier test. I checked my engine oil dipstick and it looks clean - just oil. Nothing unusual visible when oil fill cap removed. If anyone has any insight into why my coolant reservoir would have filled, blown over, not empty when cooled, only to empty out by the next morning after blowing 1/2 to 1 liter I would appreciate your comments. This has been a loyal car (other than the recent loss of A/C) and I would like to see if I can get 250,000+ miles out of her with no serious maintenance. Thanks in advance!

My '04 Cicvic SOHC (D17A2) displayed similar symptoms with a failed head gasket at about 105K. With the combustion chamber(s) open to the water jacket, coolant and bubbles of combustion gases will escape to the reservoir.

Applying air pressure to the combustion chambers thru the spark plug holes will confirm the diagnosis. The reservoir will not refill on cooldown because the reservoir system must be absolutely leak tight to function, and the breached head gasket is the opening that allows air in.

The way the system works is that when the coolant expands in the engine to where the pressure builds beyond the rating of the radiator cap (typically 15-16lbs), the fluid is released by the cap into the reservoir. Then, when the engine cools and the coolant contracts, itt draws fluid from the reservoir back into the engine. The reason for the pressurization is to raise the boiling point of the coolant beyond the operating temperature of the engine; pressurized fluid boils at a higher temperature.

I suspect that in your case the raditor cap may have failed and allowed the coolant in the engine to, as it heated and expanded, push fluid out the reservoir. Then, when the coolant in the engine cooled and contracted it pulled the fluid in the reservoire back into the engine, emptying the reservoir.

I’m inclined, being an optimist, to think you may not have a bad headgasket, mainly because if you had you’d have seen bubbles in the radiator hole when you ran the engine with the cap off. The combustion gasses blow through a blown headgasket and migrate up to the system’s highest point, which is the radiator fill hole.

The good news is that the headgasket can be definitively tested with a leakdown test, as novafan described. A kit is cheap at any parts store and easy to follow instructions are included.

The radiator cap is also easy to test, and shop can do it in minutes, or it’s cheap eneough just replace it.

Sincere best. Post back with what you find. We do care.

Hi, I have a 2001 Civic Ex with overheating issues. Originally it went in to have the camshaft sensor replaced because the car was turning off while driving on the freeway. Our mechanic has replaced the camshaft sensor, alternator, thermostat, the fan sensor, the radiator, radiator hoses, radiator cap reservoir cap (only because it blew off on the freeway when it overheated) timing belt, water pump and has checked the engine pressure to see if the overheating has to do with the head gasket but said he performed a pressure check and that the gasket was fine. Any suggestions??

Thanks for the responses.

To NOVAFAN and THE SAME MOUNTAINBIKE: GREAT INFO! I thought it odd the the reservoir did not empty on ccooling the night I brought it home. However, the next day (after testing with the radiator cap off) the reservoir DID empty on cooling. It made me think the radiator cap as well and that by opening it that had something to do with it. Would you just refill with more fluid, drive, and see what happens or replace the radiator cap first? I cannot recal the last time the cap was off…could scale have formed in there and by lossening it I “fixed” the problem? Once bad is a radiator cap always bad?

To OLICHATO2: I have had the same exact problem. There was a recall on this model year for replacement of the cylinder as a result of the car shutting down as you described. My VIN number was outside of the range for the recall. My car would “burp” when driving down the road at highway speeds. It did this from time to time over ~3,000 miles. Then one day it “burped” and died. I pulled over and shut it down. I then started it up and it ran fine until the next burp (the burp felt like it, for a split second, was not getting any gas). I dumped the CEL code and it came up for the camshaft positon sensor (I think I had to call Honda to get the reason for the code as the reader said to see manufacturer). Anyway, I kept driving as I did not want to dump much cash into a high mileage vehicle. Again, the car would shut down on a couple ocassions and the “fix” was to shut it off and it would start right up again. Finally, I bought a $50 camshaft positon sensor from NAPA and changed it myself. It did the same thing again - once. I noticed that, oddly, when driving under 65 MPH it NEVER “burped” and, therefore, never shut down on me again. Next, my drivebelt squeeled and all kinds of noises were coming from the A/C compressor. I changed the drivebelt to the short version and circumvented the A/C compressor (the compressor clutch looked like it was coming apart). I had been running at 72 MPH on the highway since and I never again experienced the “burp” and subsequent shutdown. After ~2,000 with the short drivebelt my coolant issue arose. One other thing, the “burp” and shutdowns came about one year after paying someone (big mistake) to replace a faulty alternator. About six months after the alternator replacement I noticed the battery light would flicker - for a brief second - after coasting down from say 55 to 40something MPH and upon hitting the accelerator the battery light would flicker for a brief second. That problem seemed to go away when I went with the short drivebelt but after some time came back on again from time to time - but only at the brief second when hitting the accelerator after coasting down.

In short, the camshaft positon sensor did not fix my car immediately. Driving under 65 MPH alllowed me to drive it with NO Shutdowns. And after going with the short drivenbelt I have never experiended the shutdown again while driving at normal highway speeds. It seems to be electrical in nature in my case but I really do not know for sure. It is a very odd problem and made me lose total confidence in my civic…and I love my civic. I hope the info I provided helps in some manner in your case. I’d be interested in knowing what you find. Does your car still shut down on you as you described?

Thanks for responding!

Actually my car doesn’t shut down on me anymore since we had the cam shaft sensor replaced. My main issue with my car is the overheating. While driving it home for about 35 mins on the highway it seems to be overheating. The car reaches up to 70-75 mph. The mechaninc just hasn’t quite found the problem. It is in the shop again today and hopefully they can figure out what is wrong with it. Basically the whole coolant system has been replaced. They have pressured checked the head gasket and said it was fine. Although while driving it out to the mechanic it seemed like it wanted to shut down, as if there was a cut off in the gas. When I originally took it in for the camshaft sensor they put it on the computer, because the engine light came on and the mechanic told me that it looked like we would have to check out the EVAP system but needed to focus on the overheating and turning off issue.

I have dished out over $1400 in repairs so far into the vehicle for the month of July and have also saved money in trying to install some of the parts myself. Although no matter what it keeps overheating. Is there a possibility it could be the temp sensor? Maybe something to do with the EVAP system causing a possible air pocket in the system? Heater core blockage?? I am not sure where to go next, or do I just change mechanics? I love my Honda have had it for 3 years and it has never given me problems before. It only has 124k miles on it. I am hoping the engine is not warping with all these overheatings.

Olichato2, in your case there are four things to look at next, if in fact the radiator, water pump, radiator hoses, T-stat, and radiator cap heve been replaced. Two of the things have to do with allowing the heat from combustion to escape. The third and forth are how much heat is created in the cylinders.

The first is the exhaust system. If you have restriction in the exhaust system, as in perhaps a partially collapsed cat converter or partially restricted exhaust or muffler. A problem of this sort should also manifest itself as low power, but it’ll also lalow overheating.

The second is camshaft timing. A very low likelihood, but not to be overlooked when searching for a hard-to-find cause.

The third is fuel metering. A bad oxygen sensor, MAF sensor, or such can cause lean operation. Lean operation means too much oxygen, and that has the same effect as a bellows in a fireplace…it makes the fire hotter.

The forth is an inoperative Exhaust Gas Recirculation (EGR) system. The EGR system’s function is to recirculate a bit of exhaust gas into the intake to displace a bit of air and prevent too-hot a combustion process under load. Unlike pumping more air in, exhaust gas won’t contribute to the combustion process.

Most of these should cause a fault code in a 2001. But at this point it’s best not to make any assumptions.

And by the way, it sounds like your mechanic just keeps changing parts at your expense. Perhaps a good diagnostician is in order here.

Could this also be as to why the car is running at 4k RPM’s while in 5th gear?

Nope. But something is slipping between the engine and the drive axles. If it’s a manual, you need a clutch. If it’s an automatic as I suspect, than your torque converter may not be locking up and your tranny may be overheating. It’ll be cooled by its own radiator that’ll either be part of or be in front of the radiator, and that may be contributing to your engine overheating problem.

Well it’s manual, but the clutch seems to be fine, it doesn’t stick

If you’re doing 4000 rpm in 5th gear at normal legal speeds and the car is stock than your clutch has to be slipping. That car should be doing about 3000 rpm in 4th gear (a 1:1 ratio) at 70 mph. In 5th gear it should be about 2500 rpm.

The good news is that the problem is unrelated to your cooling problem. A manual Civic doesn’t have a tranny cooler.

The car seemed to run fine for several hundred miles but then one day (while trying to blow hot air out of the defrost vents) the temperature gauge shot up to 90% max and then came down…then shot up again. Luckily, I was arriving at my destination. Later, after driving for about 25 minutes I noticed no hot air would come out of the dashboard vents, only to get a burst of hot air after running the fan on high for 3-4 minutes. I decided to replace the thermostat - about $16 including a new gasket. Since replacing the thermostat, the temp gauge has not acted up and the vents kick out heat shortly after the engine warms. Hopefully this fixed the problem.

Bad radiator cap…Bad filler neck to reservoir tank connection or hose…Blown head gasket…

It’s good to hear that you’ve solved the overheating probem, and apparently before head gasket damage occurred.

Now to get that clutch looked at.

To THE SAME MOUNTAINBIKE…thanks. It was Olichato2 that had clutch issues…issues I hope he has resolved. As for me, I plan to make my way to 250,000 miles…and, hopefully, with no problems. At 230,000+ miles it would not be unexpected to have problems but since I treat my civic well I have faith as I look to achieve my goal. I will no doubt set my sights on even loftier goal should 250,000 miles come to pass. I run 2K+ per month on average so if I’m lucky you will see a follow-up post next summer as I report on my travels.

Thanks to everyone for taking the time to post your insights. Drive safely and may any needed repairs be inexpensive and DIY!