My Honda is getting up in years now and is starting to show it. Recently the heater has started acting pretty funky. When I am driving everything is fine. Hot air is blowing like it normally should, but when I stop at red lights, stop signs etc. it almost immediately turns to cold air. This can get pretty annoying as one can guess. Does anyone have any idea what might be causing this? I have read some posts and it might be air in the lines, but im not sure. Any help would be much appreciated.

 

I have the same problem. Not as often but it does happen. It will just randomly start blowing cold air. Usually at a stop but not always. Changed out a lot of stuff but it still does it. and mine is an 05. i just learned to live with it. if someone knows the problem it would be appreciated by me as well

 

I had the same problem it was my thermostat. U might need to get it checked out.

 

head gasket may be blown,seen this before.

 

It could be low on coolant, and there's not enough to fill the heater core, block, and radiator at the same time. When you stop, the coolant will cycle through the system and exchange from block to radiator to heater core. Check your level. If it's low, it's either leaking somewhere, like from a hose or the rad itself, or as stated above, could be a head gasket. Depending on how a head gasket blows, it could get into the oil journals, or into the exhaust ports. Check your oil, see if it looks milky. If so, uh-oh, if not, check for white smoke from the tailpipe. Add coolant to the overflow bottle and see if the radiator takes it from there. If it keeps taking it and taking it, you might have a problem.

 

When these car blow headgaskets they are very small leaks(usually between #3 and #2 cylinders),what usually happens is air from the combustion chamber enters the cooling system causing an air pocket,therefore not allowing the coolant to circulate and therefore the heater core has no flow of hot coolant to create heat.You can do a leakdown test on the cylinders to pinpoint the headgasket leak.when the leak is small you may not notice white smoke from the tail pipe.

 

I got my radiator flushed the other day at it hasn't overheated every sense so try that.

 

looks like a couple threads going on about the same issue, I just posted in this one https://honda-tech.com/forums/honda-civic-2001-2005-78/i-didnt-bother-search-overheating-2682411/

I'm also having the issue with no heat when stopped/idling, but it blows really hot when driving. I changed the thermo and rad cap and bled out the system (more details are in the other thread I posted in).

If the engine is NOT overheating (temp needle stays just below half) should this be something to be concerned about? I'm going to keep an eye on things - if my head gasket is leaking it must be a very tiny hole because I don't have any leaks, coolant level is staying the same in both radiator and resevoir tank and no white smoke coming out of exhaust.

MACSI360 - did the coolant flush solve your issue with the heat being cold at idle or did it just solve your engine from overheating?

 

ive got same problem....its overheating ,,i changed themastat...a hose that had a hole in it...now its still overheating...there are no leaking fluids,,,no white smoke...an noeat coming out when i turn the heater on..it seems to over heat faster when i drive it an turn the heat on...im very lost an broke..please help

 

Did you see this thread in the FAQ's? https://honda-tech.com/forums/honda-civic-2001-2005-78/01-05-civic-cooling-system-q-overheating-fans-inoperable-etc-2889523/

 

Blown head gasket will make the car overheat!

Air pockets or insufficient level of antifreeze will overheat the engine.

 

I am having an issue of heate starts off hot for about half a min then lowers to almost cold. I changed the thermostat same thing.
@civic man mabie your water pump is broke after it heats up touch the pipes to the radiator see if there hot you can alos rev the car with the cap off and it should spary out if the pump is good if not probly bad pump

 

Overheating is not a necessary condition for having a bad head gasket. My 05 EX had the gasket go around 185,000 miles. Temp stayed perfectly at the 1/3 mark.

Inconsistent heat. Scorching hot while driving, ice cold at idle is what I had.

Find a mech that can attached a super large funnel to the top of the radiator. They will fill that with coolant and get the car up to temp. Mine had constant little bubbles coming up. Definitively head gasket. Head had to be machined.