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Honda Civic Temp Gauge HOT & A/C blows hot humid air

i have a 2002 Honda Civic EX, 155,000 miles. I’ve been having this problem for quite some time and the mechanic has not been able to figure out what the problem is. He has changed the thermostat, pressure tested the coolant (or something along those lines) but the problem persists. The mechanic also pressure tested the radiator system and said there was no leak. He also told me the tank was overfilled with water, apparently I didn’t need to be waiting for the car to cool down so I could add more water, so I’ve stopped doing that. I have NOT had the scheduled 150,000 maintenance done yet. The mechanic said it wasn’t ‘urgent’ and if I wanted to wait I could. I was hoping to spend the money repairing this problem before doing that, which he said sounded OK to him. The timing belt was replaced in 2007 right before I moved across the country.

I’ll try to be succinct, but the explanation is long. Overall: when driving the car to run errands around town the temp gauge used to quickly go all the way to HOT & the A/C starts blowing hot/humid air. When this happened I was pulling over, turning off A/C & radio & putting the car in neutral until the gauge goes back down, used to take only a few minutes but if driving in town (stop lights/traffic) i have to keep doing this b/c the needle returns to the top quickly. I also started trying putting the car in neutral while stopped at lights or in traffic & if i pushed on the gas pedal & kept the engine at 3K RPM the needle would go back down & A/C would start blowing cold when I started driving again.

The other part of this is if i change the A/C vent diverter from all vents blowing at upper body to vents blowing at face & feet or all vents blowing at feet the green ‘recycled air’ light goes out & the air starts blowing hot & humid, this persists even if I push the ‘recycle’ air button again.

Until yesterday this temp gauge & A/C issue has not been nearly as much of a problem when driving on the highway at a consistent speed, in other words when the car doesn’t have to idle the problem didn’t occur very often, the temp gauge may have moved towards ‘HOT’ but never got all the way up there. Until yesterday. I had to drive thru town with quite a bit of construction & resulting traffic as well as a few stop lights which sent the gauge go to HOT quickly. When I got on the highway I was expecting the gauge to go back down & the A/C to start blowing cold air… alas, it did not. the gauge stayed very near HOT the whole time & the A/C never blew cold air. Have I mentioned that I live in Dallas, TX? And that it was 106*F yesterday?

And yet another part of this problem, which the mechanics have told me is NOT related to this problem: in the winter time the heater took an extraordinarily long time to heat up and then would only blow warm air while the car was moving at a pretty high speed, under around 30 MPH and there was no heat, and definitely no heat when idling. I do not remember the temp gauge hanging out at HOT all the time but I do think it would go higher than the middle range.

The car has yet to actually overheat. Apparently the mechanic can’t diagnose/repair the problem until the engine DOES overheat, at least this is what he has told me. I’m not feeling very confident in this mechanic, as clearly the problem is getting worse over time. And I don’t believe it is OK to continue driving a car when the temp gauge is at HOT all the time, that doesn’t seem smart at all. Sadly, the mechanic that used to work on my car & was able to diagnose & repair problems quickly & competently has gone to work somewhere else & is no longer working on cars. So, I have decided I cannot continue to use the current mechanic and am now faced with having to take it to the dealership, something I REALLY hate to do. I just don’t know of any other reputable Honda repair folks in the area & am tired of being w/o my car for days at a time and still have to deal with the problem.

Whew, sorry this is so long. I tried to explain everything. Do you have any suggestions or thoughts about the problems I’m having? My Boxer dog is refusing to get in the car with me again after yesterday, poor guy had to ride around for over 3 hours in the heat. Thank you!

When you had the timing belt changed, did you have the water pump replaced too? I believe that in this model, the timing belt drives the water pump. If the water pump was not replaced, it may have gone bad. Your symptoms are pointing to the water pump.

Having said that, I am assuming that your mechanic has already checked for airflow through the fins of the radiator and that the fans are working. With the AC on, both fans should be running all the time.

i do not think the water pump was replaced when timing belt was done. you are correct, the timing belt does drive the water pump.

yes, mechanic said he tested airflow through the radiator fins and & fans are working. my dad & i also checked under the hood with a/c running & both fans were working all the time.

my dad kept saying water pump, too. he was just about sure that was the issue. alas, the last time we picked the car up from this mechanic my dad asked him about the water pump and the mechanic said the water pump is working fine & that is not the problem.

any other thoughts? is the heat issue related to the temp gauge & A/C not working?

When cool, remove the radiator cap and start the engine. As the engine warms up, see if you can observe the coolant flowing through the radiator. I know it is hard to do on a Honda radiator and you may have to remove some of the coolant first with a suction bulb of some type. Rev the engine a little to see if the coolant flows, then rev a lot to see if it moves. If it only moves when revved a lot, then the pump is going bad.

ha, my dad already did this! whaddya know, all this time i thought he was just poking around & faking me out! LOL

yep, the coolant moves around with a slight rev & a heavier rev. any other thoughts? i HATE the thought of taking it to the dealership.

When your dad did this, did he see any gas/air bubbles rising up in the radiator?

One more test your dad can do if he hasn’t done already. Be careful with this one. Run the car up to normal temp or a little higher.

Disconnect the ground terminal on the battery so the fans wont start up. Then reach through the fans and check for cold spots on the radiator. If large areas of the radiator are significantly cooler than their surroundings, then you need a new radiator.

Squeeze the radiator hoses and see if they have any soft spots, if so, replace them.

he’s out of town but i’ll ask him about the bubbles tomorrow when he gets back.

i’ll keep you posted as to what he finds.

i’m curious as to why the switching the air vent diverter causes the recycled air light to go off… that is a new symptom. does that mean something is blocking the air flow?

thanks for your help.

You would be blowing air out one vent and directly into another. That would not help you much.

You may have a second issue here as well. The temperature selection dial on the dash may be stripped. When you turn the dial, it has gears around the edge that turn another wheel that moves the cable in and out. The cable is connected to the heater control valve on the firewall under the hood.

Since your AC only seems to work in the recirculation position, this valve is probably slightly open. In winter when you are trying to get heat, it is still only slightly open. This car will generate plenty of heat, I can attest to that.

The outside air intake on your car is not filtered so a lot of junk like leaves, pine needles, bugs etc can get into the system and clog up the AC evaporator. That can reduce the effectiveness of both the AC and heater.

check out this other post i found while going thru ‘civic’ posts… sounds like almost the exact same problem i’m having. as i was reading the OP i thought i’d already posted my question once before.

i’m still going to take it to the dealership & hope they can resolve whatever this problem is. i need the peace of mind that my ol’ girl has been fixed properly and that any & all issues have been resolved. i need & want this car to stay with me for a long time. it is interesting that i found the post i linked to above and at least one other with pretty much the exact same problem.

as to the outside air intake, i feel certain it is full of leaves, etc falling from the trees. i used to have to park under trees and the ground was always full of leaves/pecan shells, etc. i will ask the dealership to take a look at that, too.

this is a great forum! thanks for your input, it’s very helpful. i’ve also found all kinds of great info on other car related issues. three cheers for The Car Guys! the best part is i didn’t have to call in & be on the radio! :slight_smile:

uh oh. just got off the phone with a very well reviewed local Honda mechanic (nice reviews on Yelp & on this website’s ‘find a mechanic’ files). he thinks it’s a blown head gasket. worse yet he said it may be time to trade the ol’ girl in instead of rebuilding her engine. i don’t remember exactly what he said, i heard him say it may be $2500 if they have to totally rebuild and then my head started spinning. sadness. i love this car, when she’s running well. i reckon i’ll take her in & see what happens.

This is why I suggested checking for gas/air bubbles, that is a sign of a blown head gasket. Without the gas/air bubbles, its really not likely a blown head gasket. You might also see white smoke in the exhaust.

It has been awhile since I worked on a Civic. We used to have one of the generation you own. I don’t remember if there was a bleed valve in its cooling system. We currently have a 97 Accord and it does not have a bleed valve or port.

If you can identify the thermostat housing, it will be at the end of one of the radiator hoses where it attaches to the engine, lower hose I believe, and if you can see a bolt in the middle of it that isn’t holding anything down, or a bleed valve in that location, then you may need to bleed the system.

Do this while it is cold. Just loosen the bleeder valve or remove the bolt. When coolant starts coming out, tighten the valve or reinstall the bolt. A bleed valve looks like a bolt with a chimney on top of it.

edit: I just checked the AutoZone web site and they include opening the bleed screw in their directions, but they do not include a picture of this step. I was wrong about the accord, it does have a bleeder valve in hte thermostat for some reason, the system is self bleeding. I replaced the heater hoses this weekend and just refilled the system. I checked the bleed valve this morning and there was no air bubble in it.

The Civic might not be self bleeding. I suspect that they both use the same thermostat and housing, so if one engine needed to be bled, then all would get the bleeder valve.

Follow the lower heater hose to the back of the engine. Look for a bolt with a short stack with a hole in it. It is the valve type so you only have to loosen it, good thing as there is no room around it.

edit #2: It looks like yours should be self bleeding if the replacement thermostat has a built in bleed port and that bleed port was in the 12 o’clock position when the thermostat was installed. Good idea to open the bleed valve to be sure. BTW, you have to remove the radiator cap to get the coolant to flow out the port.

One more thing, I noticed in your original post that you added water. You might get a cheap coolant tester to check the concentration of the coolant in your system. It must be at least 50% antifreeze (or close to it)

i took my car in to see what the problem is & get an estimate.

the problem is indeed the head gasket. there are a couple of other things that need to be replaced, too. i’m not sure i’m remembering what he said exactly right - the driving belt? it should have been done when the timing belt was done but most likely it didn’t happen.

the mechanic also told me my car was not going to make it to 300K miles. he said at best i’ll get another 30-45K miles if i have the head gasket & the other work done. he also said if it was him he’d trade this car in tomorrow and buy another one.

most likely i’ll have the work done instead of buying another car. the repairs are still less expensive than another car.