Coolant reservoir overflowing

It's all come down to suction. Have you tried to drink your glass of water with a defective straw? You can if you work hard on it but if the straw works 100% it'll be much easier and with less effort.

Unfortunately your radiator cap is set to constant pressure of 1.1 atmosphere and cannot overcome the loss of pressure like you would do while drinking with a straw.

Coolant going to the overfill tank uses gravity and pressure built up from the radiator however the radiator needs to work against gravity in order to bring back the coolant inside the radiator.

I got a similar issue with my 2001 Civic (187,000 miles) and my overfill tank was way over the max line I set it up while my radiator was getting empty.

A lot of people don't diagnostic correctly and don't go over the cap swap and if it didn't work, well too bad, you have to change your head gasket (very expensive). Your description of the problem doesn't make me lean toward a head gasket issue but know that I could be wrong.

I fixed my issue for just about $5 dollars. When I emptied the overfill reservoir in a clean bucket (water jug), I've noticed some black specks in it, which made me think that some rubber is deteriorating (AKA hoses).

On my Civic, I have 2 hoses joined with a plastic coupler. One side goes from the radiator to the coupler, the other side goes from the coupler to the reservoir tank nipple.

I decided that the lower hose was potentially the issue and decided to swap it (I'm cheap even though the hose, 5/8th ID was only $2.19). I also got some worm type clamp (don't use zip ties) and put them strategically.

I put a clamp where the hose connects to the overfill tank nipple, 2 on the coupler on both sides where the hose meet the coupler.

I filled up the overfill tank to the MAX line, made sure the radiator was full and went for a ride.

After 20 min driving I opened the hood and as expected the coolant was about 1/4 inch above the MAX line (coolant expanded in the radiator and it went to the overfill tank). I let the car sit overnight and in the morning I checked it again. The coolant was back to the Max line, meaning the system works as expected again.

Bottom line, don't always believe what you read on the Internet and stay logical, sometime the solution is as simple as it sounds.

Sorry for the long thread, hope it'll work out for you the same it did for me saving you money on the way.

Enjoy!

I had a overheating problem and noticed that:
1. Coolant was flowing out from reservoir.
2. Coolant not topped off in radiator.
3. Steam or white smoke from tailpipe

I topped off coolant after engine cooled down and removed air bubbles. I proceeded to drivea nd after a while, the temp went upagain. So, I turned on the heater and temp went down while driving.
I noticed that I still have:
1. Power
2. Fuel mileage still good
3. No smell of coolant from exhaust or interior

The next day I checked for signs of a blown Head Gasket and Radiator leak by checking for:
1. White smoke from exhaust (tailpipe)
2. Milky residue in dipstick and under oil cap when
engine was cold
3. Discoloration of spark plugs
4. Discoloration of coolant
5. Leaks around engine and connecting hoses
6. Spills under car
7. Radiator fan turning
8. Both radiator hoses had the air sucked out
(imploded)

I then replaced the coolant, thermostat & radiator cap

All I have now is:
1. Steam or white smoke from exhaust (tailpipe)
when idling (even after engine is warm, but
disappears after I drive it around)
2. Coolant fills up when idling, but overflows from
reservoir only while driving
Also, my engine doesn't overheat anymore.

Please help!

I have a 1.7 L, fwd, at 2001 honda civic ex sedan

Today my 97 Honda Civic overheated. The radiator was cold. This radiator is only a year old. Why is this happening and what to do?

Car temperature was in the red zone. Smoke was coming out from under the hood. Coolant was dripping all over though the coolant reservoir was full. Checked hoses, saw nothing loose or cracked. Radiator was cold to the touch.

I just had this radiator replaced only about a year ago.

Sounds like the coolant is not flowing, check the thermostat and check the water pump if the rad was clogged half would be hot and the other cold. Did you do anthything to the system like flush you can try that just make sure you get all the air out.

Thank you
Two Lane

Just a couple months ago, I noticed a strange white foam puddle forming under my '98 Honda Civic EX coupe. I checked under the hood to find foam bubbling out of the reservoir cap. While driving, no indicator lights are showing, and temperature reads normal. I have to constantly add distilled water to the reservoir. At the same time, the car seems to be either burning or losing a lot of oil. After 3 months from changing, less than 1 quart remains in the engine. Engine smells bad after just a few minutes of use. Could these be related or completely separate issue? How to fix?

Thank you for your prompt response! I will attempt your ideas immediately.

I recently flushed my coolant system and have been driving my car for about a week but today it decided to leak coolant to the point of overheating. When I opened the hood it looked like it was leaking out of the coolant reservoir or the reservoirs lid. It was also spewing white smoke out of the exhaust. Does the reservoir need to be replaced? Did the lid just come loose? Would this cause my problem?