Ok so I have spent about two weeks searching and reading old threads on symptoms that cause over heating so I have already done some extensive searching. The car is a 1999 Honda Civic DX hatchback with the D16Y7. Car is bone stock. It all started when I checked my coolant one day for regular checks and noticed my radiator cap broke(the coolant got very corrosive). Nothing fell in the radiator, I was able to pull it out. Well at this point I decided to change my thermostat if the coolant had gotten this corrosive. So I got a thermostat from autozone, changed it out, got a radiator cap from Honda and was on my marry way. Well the car started to over heat for no reason whatsoever and when I would pull over, my coolant over flow reservoir would be overflowing.

I tried burping my system a few times and thought I got more air out but the car kept over heating. I should also add that sometimes the heater would blow cold, not hot at all. Well at this point I did some research and people were saying its the headgasket and that I should have it checked out for exhaust gasses in my coolant. I took it to a mechanic and had the coolant checked and they found no gasses in the coolant and they said I should get a honda thermostat and new radiator hoses. So I did, Honda thermostat and new upper and lower hoses.

When the parts came in, I took the radiator and old thermostat out and flushed the system with the heater turned on with a water hose for about 5-10 minutes. Nothing but clear water was coming out towards the end. I then installed my Honda thermostat and new hoses and filled it up with Prestone 50/50 coolant. My buddy and I sat there for 1 hour reving it the motor to get air out, along with a funnel on the radiator filled up to get all the air bubbles out and after about 1.5 hours, we figured it was done. The fan would turn on, thermostat would open up. Everything working perfectly.

It has been two days since I did all this and today the needle jumped to 3/4 on the temp gauge. It then dropped down to a little above half. When I got home I opened the hood and the reservoir overflowed again and the fan wasn't turning on with the needle at 3/4. After a minute of idling the fan turned on and stayed on for a long time, car never cooled down and never got hotter so after a minute or two I shut it down.

I then opened the radiator up with a towel over the cap and the system was heavily pressurized of course. But I did notice when I would relieve some pressure through the cap, it would want to suck in some coolant from the reservoir. By the time I opened the cap, I could see the top of the radiator core and there was not any coolant towards the top.

I turned the car on after draining the reservoir into the radiator and some spilled out when i started it. I let it idle for a bit and then the fan came on (all of this with the radiator cap off). The fan circulated a few times and when I gave it some gas, you could see the coolant moving in the radiator. So I placed the cap back on the radiator and drove around the neighborhood in first gear around 5k rpm to see if I could heat it up and pressurize it and the needle stayed half way and did not over heat.

So what the hell is going on?? I am seriously stuck. I don't think its the headgasket, but if it is I can do all the work, just not really wanting to if I don't have to. I guess I will make some "cliff-notes" from my novel here to break down the basics.

Cliff-Notes:

• New Honda Thermostat
• New Honda Radiator Cap (1.1bar)
• New Honda Upper and Lower Radiator Hoses
• New Coolant
• Mechanic tested coolant for exhaust gases, results were negative
• Car only over heats when system is pressurized (with cap on)
• Heat sometimes blows cold
• No coolant in my oil and vice-versa
• Car has 135k miles, regular maintenance, never a single CEL/MIL light.
• Never heated car up to "H"
• Radiator fan does turn on, but is delayed from turning on when heater blows cold.
• Sometimes when I open the radiator cap and squeeze a hose, it seems to drop the coolant level and makes a sound like releasing pressure or a bubble.

Please if anyone can give me some insight I would greatly appreciate it. I feel so lost, I have searched and read threads from 2004 and have tried everything, but the headgasket. I hope this isn't to much text, I like to be as thorough as possible. This is my daily driver so I need to find out whats going on.

 

I feel your pain man, Iv been going through the same thing with my crx. I said **** it and replaced the headgasket just to be extra sure, sometimes its just easier to fix one thing and get that out of the way then to trouble shoot for hours on what the hell is going on.

to me it sounds like your car is being a pita and has air bubbles in the system. they will cause intermittent overheating when one sticks right by the thermostat and wont allow it to open. jack the front of your car up as high as you can get it and burp the system until its just water. do you have a bleeder valve on a water neck, I made a funnel with a hose duct tapped that goes in it so I can pull the bleeder out and have the funnel 8" about the head full of water and keep squeezing the radiator hoses till no more bubbles come out, it may take a few heat cycles to get all of them out

 

if the system has been bleed, then the only other thing is a HG leak around cyl 4 or 1.. does the res bubble after the car is warmed up?

 

When I turn the car off and open the hood. The reservoir usually bubbles. Sometimes it doesn't. When the car is overheating, the reservoir is full and bubbling.

 

Try going with a mixture of 70% water and 30% antifreeze. This will keep the car cooler.
what is the condition of the radiator?
How old is the water pump? Corrosion may have destroyed the impelled on it. Its probably corroded, pitted, and warped. A bad pump will not circulate coolant very wheel. It will sort of just cavitate the coolant. No bueno.

 

Radiator is as old as the car. End tanks are not cracked, fins are what you would expect for a 12 year old car. It never caused problems before I changed the thermostat.

Water pump is original as well, have not changed that either. With the radiator cap off you can see it pump coolant pretty well so I don't think flow is an issue.

 

are you sure your thermostate is opening ? maybee it stuck shut pull it back off and check it

 

Remove the thermostat completely. Its not needed in warm temperatures anyway.
Do this along with running a 70-30 water to coolant mixture and your needle should stay on the cool side regardless, unless you have pump failure or a radiator that's passed its lifetime.
antifreeze has no cooling properties. It has 2 functions: prevent freezing (a property of glycol) and prevent corrosion. Many race cars will run a 100% water with a glycol additive. Know what diy'ers use? Hand soap

 

Yes I am sure the thermostat is opening, both hoses get warm.

I tried the no thermostat scenario on my 89 hatch with a LS swap and the results ended up being the car ran to cold. There was not enough time for the coolant to collect the heat from the engine so I was still not cooling. I have been putting nothing but water in when it needs more, other than dumping my reservoir back into the system.

This morning I drove the car in 80 degree weather to and from school, about 12 miles one way and the car did not over heat. When I got home, the coolant reservoir had some coolant in it (I left it empty last night) but was still below the minimum mark.

I want to believe there is something about the heater core that is acting the system up, maybe an air bubble or something. I don't know why else the heater will blow cold sometimes then hot another. It just doesn't make sense. My heater valve does work, I can see it working when the hood is open.

 

its a HG leak, your blowing compression back up through the hoses, you have a leak around the waterjacket.. probably cyl1 most likely..

 

Do a compression test followed by a leakdown test, if the results are unusual.

 

Will try some things tonight. I have driven the car around all day today and has not over heated. Also has not spit up any coolant into the reservoir yet and its 94 degrees out. It is weird, it is like it intermittently fails which makes this more difficult.

 

Temp the same on both heater hoses?

Any white smoke on start up?

If you don"t have a compression or leak down gauge check the piston tops for coolant after a over night engine cool down. You might even see coolant colored droplets on the spark plugs.

 

ANTIFREEZE has 2 objectives. 1 lower freezing point so water does not freeze. 2 raises boiling point so water does not boil. Less antifreeze means hotter water, so how is putting less antifreeze in your system gonna make the car run cooler.

 

No white smoke, pulled plugs tonight and they were clean, just worn from some mileage so I threw some new ones in. I looked in the cylinders and they were fine too, no signs of coolant or anything.

I raised the front end of the car a good 3' off the ground and burped some bubbles out then ran the car changing between revs and the coolant never gushed up or blew up or anything. Drove 16 miles home and when i got home the coolant reservoir was below the max level, left the shop with no coolant in there.

 

Wrong....raising the boiling point of your cooling system is NOT the purpose of antifreeze. Like I said, anticorrosion, and antifreezing are its goals.

On paper, yes antifreeze has a higher boiling point than water. HOWEVER, its ability to transfer heat is less than water. So, the more antifreeze you put into a vehicle, the higher its boiling point, but the hotter it will run due to it not being able to transfer heat away from the motor as well as water.

A well running cooling system should never be boiling even if it is 100% water. Water boils at 212 degrees ATMOSPHERIC PRESSURE. However, its boiling point is increased when pressurized, hence why the cooling system is pressurized.

This is not my opinion. It is science.
Anything else?

 

Took it to another shop today, it is the headgasket. The guy placed a test tube thing on the radiator cap opening after it warmed up and you could see the bubbles and the dye changed colors. I ordered all the stuff including new studs, water pump, timing belt and tensioner for a week of fun. Yes, I am having the head resurfaced. Just wanted to post up what I finally did. Will post up end results once the car is put back together again.

 

Damn, you're halfway to the cost of a B swap in parts/labor.

 

Well I am building a B18C1 for my other car currently, far more pricey. Plus this is my daily, gas mileage is awesome. Don't want to mess that up. Plus if it ever gets stolen, I won't be done a twin cam.

 

All very valid reasons. Understandable