My wife's 2000 Civic LX overheated the last 100+ degree day we had here 10 days ago. She noted going up a steep hill with the A/C on and rough idling and shaking. She pulled over and let it cool down, then she was able to add 1/3 gallon of water before returning home.. No issues. When she got home I noted both upper and lower hoses were hot and all fans were running. Overflow is working properly, small amounts would drop into reservoir from time to time. I checked her radiator cap and the small plunger gasket for overflow was falling apart a bit. I replaced the radiator cap with a spare 0.9 from my 2001 Corolla. The Civic cap is noted 1.1....... I don't think this would make much difference until Im able to get another Honda cap. Her car has ran fine since then, but now will idle rough at cold start up for about 10-15 seconds... Other than that the car runs fine. Could it be the new cap? Any idea why it overheated in the first place? Thanks!

 

There's an issue with it overheating, and you think its fine as it is?

 

Read it again, please. Anyone else with some helpful info?

 

I would rent a block tester to test for combustion gases in the coolant.

You mentioned adding water but never mentioned what has been running in the cooling system. Prior to your wife adding more water, was the system full of at least a 50/50 mix of Honda coolant and distilled water?

Now that it has overheated, the head possibly warped enough to allow the one or two combustion chambers to leak enough until it warms up and reseals to hide the problem. There is a pretty decent chance the problem will get progressively worse over time until the head is removed, resurfaced to a true flat surface and a new head gasket installed.

Running anything less than 50/50 coolant to water can allow premature boiling as water has a lower boiling point than coolant.

As well as if the radiator cap is faulty it could potentially allow air into the system which also could cause hot spots and over heating. An air bubble in the area of the fan thermo switch would prevent the fan from kicking on and allow an overheat.

 

Ditto what TomCat39 posted all of it. 94

 

Yeah I read it. Your wife ran the car while it was overheating. Worst, uphill. Meaning she stress the hell out of that D while going uphill. It may drive fine, probably meaning to you that it didnt' overheat again, but no its not. Running rough could mean only a couple of things, ignition, not enough fuel, or not enough compression.

 

Thanks, good info here. I changed the coolant with a 50/50 mix last winter, but it was NOT Honda brand. Since she only added less than 1/4 of a quart of water and no signs of coolant loss, I'm hoping the thermostat just stuck closed for a short while. I did have her tap on the thermostat before she proceeded with her trip back home.

 

We had a heater hose blow today. I got it to a nearby shop so they could test the block.. The liquid turned green/yellow, so the head gasket is bad.

Picked the car up yesterday, was able to get it home without overheating. The shop replaced the heater hose and coolant. I checked the spark plugs when I got home.. The two closest to the timing belt had bleached tips the worst. The two plugs near the distributor had oil on the threads, also white tips but not as bad. Probably wont get good feedback on this, but I used blue devil head gasket sealer and did the whole process (removed t-stat, idle car for 50 minutes) then I drained fluid and cycled again with water.. Drained fluid again and then added fresh coolant. I am going to rid the system of air today after work and take it for a ride.. I am hopeful for no overheating. We had planned to get rid of this car soon, but not this soon. If this blue devil will get us through a couple of months, I will be happy with that. Thanks for everyone's replies on this thread thus far.. I will update more info later.