ok.................i have an 01 civic ex. when im driving @ high speeds (i.e. 50 mph or above) my heat works fine. when slowing down (i.e. 40 mph or below) my heat will blow cool and i will overheat. i have replaced the thermostat twice, and i have drained and refilled the antifreeze twice. i work @ an auto repair shop ( go figure) and we just hired a "master mechanic". this "master mechanic" is basically telling me im an idiot. when i tell him all my symptoms he says theyre all normal. i tell him that when i slow down my heat blows cold and he says thats because im not letting my car heat up and that its normal for an engine that size to take 20+ mins. to heat up. hes also telling me that my temp. gauge should stay well above the half mark while driving. hes also telling me that when my heat starts blowing cool and my temp. gauge rises its not because im overheating (because if that were the case i would see steam) but because my gauge is broken. im telling him thats wrong. i have an accord that takes 5 mins. to heat up and the gauge stays well below half. he laughs like im an idiot and just keeps saying the same things. can anyone help me please????

 

That "Master" Mechanic is an idiot... Your temperature gauge should be a little below the middle.

Maybe get your heater unit/blower checked? Idk

 

im having the same issue and im as clueless as you. this weekend im going to take the water pump off and check it if it seems ok im pulling the head off and replacing the gasket. ive changed the thermostat, radiator cap, radiator, cooling temp sensor, fan switch, and cluster trying to figure it out, there are alot of people on this forum that have posted the same symptoms and have not posted solutions.i even pressure tested the system on 16psi for about 6 minutes and it held.. if you do figure it out please pm me. if i fix mine ill tell you what it was..

 

I had the same exact thing on my car. I even made a topic about it.

https://honda-tech.com/forums/honda-civic-2001-2005-78/over-heating-problems-05-ex-2618748/

But I guess you are in a whole different story if you have already changed the thermo + changed the anti freeze.

Just curious, how much mileage do you have on your car ?

 

I too am having the Same problem for awhile. Couple weeks back I did a flush and changed my thermostat. My car was not overheating for awhile, until yesterday morning my car started to overheat. After the drive I opened my radiator cap and air was coming out so I added more coolant. Then today I drive to work their was no overheating but when I opened up my hood my coolant resovoir/bottle was filled up to the top. Could this mean theirs still air in the system or could it be something else?

 

when you filled up your radiator did you let it bubble up and fill it up little by little? you might have to do that so theres no air

 

So when I'm driving home from work my car doesn't overheat on the way home. When I opened up my hood their was some coolant around the radiator neck. Then I opened up the radiator cap, air was coming out. I'm thinking it could be the radiator cap not holding pressure. But does anyone have suggestions? I'm going to keep this updated.

 

I've been having the same issue with no heat at idle so I figured I'd share my input..

This all started a couple months ago. The heat is fine whenever I am driving but when I come to a stop in traffic or at a light it gets cold. This is the 3rd year I've owned my car and I never had this issue until this winter - 2002 civic ex

The car does not overheat at all, the temp guage stays a little below half the entire time. A couple times the coolant bubbled up and overflowed from the reservoir - not sure what caused that to happen. Never did the car overheat and when I idle/rev it I do not see white smoke out the exhaust.

I changed the thermostat and radiator cap - when doing so I did what people told me and ran with cap off until fan turns on/off to get all the air out. Since then the radiator has been full, the reservoir tank has not gained or lost any coolant in it (its about 3/4 full I know I should drain it out but I havn't had time to do so). There also has not been any coolant bubbling out.

I know the new thermo works because both top and lower hoses get hot, fan kicks on/off, and the temp stays at normal slightly-below-half position.

Like everyone else I'm stumped as to why it still loses heat when idle. Could there be a block somewhere or could the heater core be going bad?

Last summer I had the timing belt & water pump done at a honda repair shop (about 120k miles then, now has 130k miles). Everything else runs fine and as I said I don't see any white smoke out the exhaust nor do I have any leaks of any fluid.

Anyone got any suggestions or ideas? Hopefully this info helps the thread out.

 

Sounds like the head gasket, do you smell coolant in or out of the car?


Edit: I have an ex 03 that did the same thing and it was the head gasket!

 

that's exactly what I am hoping it isn't. No smells of coolant, no coolant or oil leaks, no smoke out the exhaust. I'm stumped...

 

Well mine didn't do the whole smelling thing at first, it just overheated. I let it go and then after two weeks I started smelling it in and out of the car. However it was an easy fix. Pulling the head and replacing it was rather simple. other than the waterpump, I can't imagine what else it would be. I wanted to add that low coolant was another sign that it was the head gasket as it was seen on and around the head where it mounts to the motor at least for me.

 

Hi guys,I have responded to several Civic overheating threads,I can tell you what I have been seeing on these cars.
most the time if the car is overheating I have rarely had a thermostat fix it,9 times out of 10 i end up putting a head gasket on,I always send off the head to be checked,these heads can become warped easily(although most of the time the head is ok).I believe honda came out with a bulletin on some models with heater cores becoming clogged and the car will begin to lose heat at idle.I will check on this tomorrow when I get back to work.
Things I would check in this order
coolant level,check for leaks,coolant smell.Pressure check system.
bleed coolant system
coolant fan operation
thermostat(is the upper and lower hoses warm after car has warmed up)
perform compression check
inspect spark plugs,see I 1 looks different from the others,white/greenish tint
perform cylinder leakdown test
head gasket,have head check for warpage.
I dont know why I seeing this more often than I used to,maybe since these cars are getting older.Good Luck guys.

 

head gasket. or you have an issue with your heater core not flowing coolant correctly or it has an air pocket. but most likely sounds like a head gasket.

 

Thanks for the replies. Earlier this evening I burped it for a 2nd time - the fan ran three times and on the 3rd time no air bubbles came out. Something is pulling air into the system - most likely head gasket but I hope it's not the case.

Tuesday my civic is getting the recent air bag recall fix, the dealer said they will check it out and see if the gasket is going (leak down test I assume?).

 

I'd just like to say that it's a good idea to periodically check this even if your car seems to be running okay!

I had no problems whatsoever. My heat worked at idle and at speed. Temperature sensor seemed to be working properly. It never went beyond the middle of the temperature gauge, never overheated or lost any coolant. One day in the drive-thru I realized that I never heard my radiator fan come on. When I got back home I popped the hood, touched the bottom radiator hose and it was ice cold.
I removed and tested the thermostat and it barely started to open at ~185° F and never opened more than maybe 2mm at ~200° F.

I drained the radiator, replaced the thermostat (and gasket) and burped the system. Everything works like it should, now.

Keep an eye on this before it leads to problems!