Rep Power: 0

This issue has been happening for a while, but now it has become a bother because of the colder weather.....

When I start the car, for the first 10 minutes or so, the air will not blow hot , regardless of coolant temperature. Even when the engine is warm or at operating temperature, it does not make a difference.

Then, all of the sudden, with no change, the air will blow as hot as it should and work just fine.

Is this a heater core or thermostat issue? Neither have ever been replaced.......thanks in advance!

 
Rep Power: 811

after car is fully warmed up, park the car (leave it running) and start feeling coolant hoses. the upper and lower large hoses should both be hot. lower hose can be less hot than the upper on a cold day, but not cold or warm. if both are hot, thermostat is good. now feel the two smaller heater hoses going into the dash at the back of the engine bay. they both should be fairly hot. if one is cold, you found the problem. the heater control valve nearby is stuck in closed position. have someone turn the temp dial from full hot to full cold a few times and see if the valve moves. if not, bad valve. you can try spraying it with silicone, but more likely it needs to be replaced. it has usually a blue cable attached to the valve, kinda like a smaller throttle cable. you can also peek in from under the driver dash where the gas pedal is. look up towards the radio and you will see a bunch of plastic gears. turn the temp dial hot to cold several times and watch the gears. they should be moving each time you move the temp dial one click. they will not move super smooth, but they should be moving.

 
Rep Power: 0

OK so the vehicle was cold when I began. I checked the coolant (no reason for me to suspect it to be low) but it was! I will top it off tonight. Vehicle has been running below half way on the temp gauge, and the over flow tank was at MAX. It is just low in the radiator.

....vehicle was cold, engine was ran till operating temp, heat was on hottest and full blast. I checked the gears by the gas pedal and they checked out good. I also checked out the heater core valve, and it moved in conjunction with the hot/cold know so that was good.

After 10 minutes of vehicle running, and operating temperature achieved, the air was still cool, and the BOTTOM coolant line was still cool. The thermostat never opened, which is really wierd because it was at operating temperature.

As soon as it was driven the thermostat opened and the air got hot. When I stopped, all the coolant hoses were also hot. But if the thermostat was broken, wouldnt it overheat or not turn on at all? The test would lead to the thermostat, but like I said, as soon as I drove it, the air got hot and stayed hot.....

Ideas? I dont mind replacing the thermostat because it is so cheap, but it is still kinda wierd that it is working, but not working LOL

 
Rep Power: 811

its possible the thermostat is barely sticking closed but when you drive and the waterpump starts moving coolant around much faster, it pops open. now im not sure this would cause a problem with the heater blowing cold, because the heat lines in the dash come directly from the engine block i believe. this is why if you start overheating due to a bad thermostat, you can turn the heater on and the coolant will lose some heat that way (independent of the main radiator). the thermostat's only function is to let coolant circulate to the radiator when the temp gets too hot, and close it off when the temp is not hot enough. thermostat should be constantly opening and closing as the coolant temp changes. its very easy for them to malfunction. and always use a honda oem thermostat if you want to replace it. its possible that your heater core in the dash may be clogged as well. hard to say for sure.

 
Rep Power: 0

I kinda ruled out the heater core because if it was clogged, it would work more intermittently. However, the problem is always the same and the heat will always work once it has started working. It is only during initial start up does it become an issue. I am going to top off my coolant and see what happens.....if it still is messed up, I think I will replace the thermostat and see what happens. I'll be sure to report back.

 
Rep Power: 0

Is the thermostat number 14? Wanna make sure I get the right part number....

http://www.hondaautomotiveparts.com/...y5=HEATER+UNIT

 
Rep Power: 811

no that is the assembly in the dash with the gears. you want the thermostat in the engine compartment cooling passages. #5 and it includes the gasket

http://www.hondaautomotiveparts.com/...+PUMP+-+SENSOR

 
Rep Power: 0

Is there a secret search button on hondaautomotiveparts.com that I dont know about? I always have such a hard time finding anything unless I know exactly where to look!

Anways, I got home, let the engine cool, and topped off the coolant. I didnt exactly measure the top-off amount, but I know I put atleast a quart in. The whole system holds 4.2 quarts (just over a gallon), so I was WAY low on coolant obviously.

When I was sure the radiator was completely filled with coolant, I fired the engine up and surprise surprise, the heat came right on as soon as the temp gauge started reading.

Does this seem to make sense? I am very surprised because like I said, my overflow tank was at MAX and my engine temp never got even close to half way up the gauge. I guess I assumed that with that much coolant missing, there would be more signs.

Is it possible some leaked into the tranny? I'll be looking into that tomorrow morning......

 
Rep Power: 192

Yeah that's pretty low. The engines don't take much to cool, especially if it's getting cooler where you live.

It is weird that the overflow is at max, it should be empty if the cooling system is low. The radiator cap is what controls the coolant entering/exiting the overfill so I'd replace that with an OEM cap. Pull the overfill hose off the radiator and make sure it's not clogged.

Our cars have water control valves which means there is no coolant running through the heater core until we turn the climate control to heat. Maybe the low coolant effected that, I'm not sure on that one.

Have you had the coolant flushed recently? The car will burn off some coolant, it would take awhile to lose 1qt though.

 
Rep Power: 0

I did the coolant flush about 50k miles ago and I am [I]pretty sure[I] I checked it a couple of months ago. I usually check the overflow tank because when I am thinking about my fluid levels, the engine is usually hot. I know the overfill hose is good because while I was topping it off last night, I saw some fluid burp into the radiator.


UPDATE:........I AM AN IDIOT! LOL; problem solved: low coolant. I feel like an idoit but I guess it was so obvious I missed it. I started this post because I wasnt sure of how to start my troubleshooting even though I knew what components could be to blame. As always, you all have assisted in another cost effective solution to my car troubles =) Thanks again guys!!! Cannot thank you enough.....

Alex

 
Rep Power: 192

Yeah most people just check the overflow.

I'd still change your radiator cap, it seems like it's been messed up for awhile since the coolant was that low in the radiator yet the overflow was full. The level coolant in the overflow should change depending on engine temp. If it's hot the fluid expands, radiator cap releases some coolant into the overflow so the pressure doesn't get too high. When you shut the motor off the coolant cools down and the radiator cap lets coolant back into the radiator to keep it full. It does this every time your motor heats up/cools down.

Once the coolant gets low this process is no longer takes place because there is room for the coolant to expand inside the system. The radiator cap may be working fine now but I wouldn't trust it for the long term.

Make sure you get an OEM cap.

 
Rep Power: 0

GTG.....they are $20, I am going to pick one up today.

 
Rep Power: 811

+1 on the radiator cap. you should never have to fill coolant in the radiator, only the overflow tank (unless doing a coolant change). i think that will solve the rest of your problem and the coolant should level out after that with the radiator full and overflow tank at max.

 
Rep Power: 0

I am replacing the radiator cap for sure....but the whole system is kinda wierd because the overflow tank has remained full for the most part. But right after I got hom yesterday, let the engine cool, and began adding coolant, I noticed the overflow tank was at MIN. Regardless, while the overflow tank was at MIN, the radiator still took a quart of coolant so.......

2k miles to 200k miles and she is still running great; cant complain! =)

 
Rep Power: 192

Yeah either the radiator cap got stuck for a time or the system wasn't properly filled when it was last flushed. It takes some running time for the air to get worked out of the system and that effects the coolant level. Most of the quick oil change places will ask you to come back a couple days later so they can verify the level.

If the coolant is low enough the vacuum in the system might not be strong enough to pull the fluid out of the overflow.

Either way at 200k it's time to replace the cap, even if it wasn't the problem.

Probably time for a flush too, make sure Honda coolant is used.

 
Rep Power: 0

I am going to wait until the Honda recommened 60k mile interval till my next coolant flush. I did the flush myself so I know it was done properly....I am quite familiar with getting the air out of the lines; I guess it must have burnt off or something.

Anything else you can think of for a good 200k service? Timing belt, water pump, spark plugs, filters, struts, brakes (pads and rotors), EGR valve, charcoal canister, EVAP sensor, O2 sensors, tires, clutch, tranny bearings, and fluids are all good.........

 
Rep Power: 811

these cars have extremely small radiator and cooling passages. it needs to be bled so most of the large air pockets get pushed out. the smaller ones will work their way out over the next year or so. if everything was filled and bled correctly, the overflow should be right around max when cold, and right after driving it should be above max by a few inches. when it cools again it should go back to max. the max line is not the hot level like some cars. its the cold max. same with all the other fluids like brake and ps fluid. only trans needs to be checked hot. and if the cooling system is working, the radiator should always be full. anyway hopefully it was just air and a new cap will fix it all. if you still see coolant loss, its the start of a slow headgasket leak.

 
Rep Power: 0

I'm kind of having the same problems. I'm trying to fix this for my fiance so she can have heat this winter.
Problems have been continuing for a few weeks now. No heat will come out of vents until maybe 15 minutes after the temp gauge is in the middle, and even then, its not that hot and it doesn't last long. The heat has been very intermittent. She had the car in to the honda dealership last year and they ran diagnostics and tests and said nothing was wrong.
I have drained, flushed, and replaced the coolant to the correct level. After running the engine up to the mid range on the temp gauge, still no heat from the vents. I drove the car around town and then back to the house and checked all hoses. The two hoses from the radiator were both cold, and the inlet and outlet hoses to the heater core were both cold as well. The heater control valve opened/closed appropriately when temp dial changed from inside the car. No leaks were ever found either.
Bad thermostat? Heater core?
Any help is greatly appreciated.

 
Rep Power: 811

wow both hoses cold! i cant say ive ever seen anything like that. at the very least the top radiator hose should be hot because coolant is coming directly from the engine block. either you are way low on coolant or the water pump is toasted and not even turning (which is odd because these are belt driven pumps). is the radiator full of coolant and the overflow tank on max? does the temp gauge go above normal when driving it? i think first you have to figure out why coolant is not even coming out of the engine. then see if it goes thru the radiator and the thermostat is opening (bottom hose hot). after that, either the heater will start working or you have to troubleshoot the cabin heater hoses or core.

 
Rep Power: 0

radiator is full and overflow tank was at max when cold. after driving it for a few minutes at normal temp, the levels remained the same.
the temp gauge used to go up above normal while driving occassionally, but it would return to normal pretty quickly. at that point she would get a few minutes of heat.

i will take the car out for a longer drive tonight or tomorrow morning and then check the hoses again, and see if any get warmer than they were today after the short drive

 
Rep Power: 811

yeah the top hose at the very least should be too hot to touch after 10-15 mins of driving. if that happens, then you can try replacing the thermostat with a new honda part and then see if the lower hose is also getting warm to hot.

 
Rep Power: 0

ok. so today i did as much as i could with the tools and time i had available. i drained the coolant, took everything apart, and replaced the thermostat. i put everything back together, and replaced the coolant to the proper levels.

took the car out for a 10 minute drive. temp gauge went all the way up to HIGH and still no heat from the vents. got back, checked fluid levels, and all was good. top hose from radiator was almost too hot to touch, and lower hose was hot as well but not as hot as the top hose. top hose to heater core was hot and lower hose was cold.

so now i'm suspecting a blocked/bad heater core. would that also cause the temp gauge to go all the way up to HIGH and the car overheat??

 
Rep Power: 811

no the car should not be overheating in that case. like if you turn the temp dial to cold, it will close the valve and coolant will not circulate to the heater core, but you should not get overheating because thats what the radiator is for. did you bleed out the air bubbles after changing coolant? the radiator hoses being hot is a good sign that coolant is moving thru the system. but almost always you will have air bubbles and it can cause the ECT (engine coolant temp sensor) to read incorrectly because it is not touching coolant. so it looks like you are overheating when in reality everything is fine. drive the car around til its fully warmed up. park car on a steep incline so the front of the car is pointing up. open hood, very carefully wrap the radiator cap with several shop towels and open it. once it depressurizes, remove the cap and mop up spilled coolant. turn on the car and set the heater to max HOT and turn the fan on one notch. watch the radiator to see if any air bubbles are coming out and popping. if the coolant goes down, add more so that the level is high enough to see. you may need to do this for 30 mins or more so that a majority of the air is purged. squeezing or gently hitting the upper and lower radiator hoses will make the bubbles come out faster, as will revving the engine to 3k rpms occasionally. keep a few towels around the hole in case some coolant overflows. eventually heat should start filling into the cabin from the vents. keep going until you no longer see large air bubbles. keep the radiator near the top. after air is gone, put the cap on tight and turn off the car. go for a drive and turn the heat full blast while driving and make sure hot air is blowing. park the car and let it sit overnight until cold. check the overflow tank level and make sure it reads at max.

 
Rep Power: 192

Yeah I just did this yesterday and it took me about 15 min until I stopped seeing air bubbles coming out of the radiator. I did exactly what gearhead said, car on an incline (jackstands for me) and giving it some revs every now and then.

If you filled it up and drove w/out doing this bleeding process I'm sure this is your problem.

 
Rep Power: 0

thanks gearbox. i did everything that you said. after about 30 minutes i didn't see or hear any more bubbles. at the beginning there was a lot of air coming out.
temp gauge was right where it was supposed to be. all hoses felt perfect. even the outlet hose from heater core was warm but cooler than the inlet. i drove the car after following the directions and the air coming out of the vents was extremely hot, and stayed hot. i will check the coolant levels tomorrow morning, but i really feel that the problem is now solved. i'll post again if there is any else that comes up.

thanks again for all your help!!

 
Rep Power: 811

sounds good, and yeah the return hose from the heater core should feel warm instead of hot if the fan is turned on due to the heater core acting like a mini radiator.

dont forget to check the overflow tank coolant level in the morning. you may need to fill it back to max. if its too low, you can suck air back into the system and have to do everything all over again.

 
Rep Power: 0

Gearbox, what do you think of my issue? Thank you in advance.

My 1997 civic:

• Hose on top is hot
• Bottom is cold
• Heater control valve hose is hot
• Outlet is hot (not as hot as inlet) at firewall

I flushed with water and air. I also used CLR, but only could get 8 or less ounces in; not sure about that issue.

based on the threads, I will change my thermostat, even though it shows normal operating temp on the idiot-guage.

Started to tear down the dash for the heater core, but will change the thermostat first - I was told that it is not the thermostat due to it showing normal range on the idiot-guage.

 
Rep Power: 0

Thanks for all the suggestions. I'm having a similar problem with my 2003 EX, except it seems my air conditioner is engaged (due to engine revs) until the engine heats up, although the air button light remains unlit. I had a similiar problem with my 2009 Accord which ended up being a defective relay in the engine fuse box. Could my Civic problem also be a defective relay??

 
Rep Power: 252

If your car doesnt warm up your thermostat is bad.