Heater issue

[FG3_drv]

Hi everyone,
Weather is getting colder here in the NW (oregon), and I've noticed that I have an issue with my heater. It seems to work fine while i'm moving, blows super hot air when on max setting and I have to turn it down sometimes. However, while standing still or moving less than 20mph it starts to blow cold/tepid air out of the vents on max setting. Engine generally takes about 10-15 or so minutes to warm up while driving. And i've noticed a decline in fuel mileage during this last fuel up, although not significant but noticeable. From 28.9 to 26.2mpg. The latter makes me think t-stat, but due to colder weather and worsening traffic due to holidays I can't tell. Car has 41k and I've had it since september so I don't know what normal is for this car yet, haven't really established a baseline in colder climate. Outside temp in the mornings was around 32 F a few times and generally it stays around 40 F during day. What does not add up for the t-stat failure is that heater works while driving, even on highway. Usually, when t-stat stuck open engine temp decreases and heater starts blowing cold but this is complete opposite. I replaced cabin filter a month or two ago, coolant is at the neck of the radiator (honda blue), 41k on engine, coupe EX. Not having an actual temp gauge makes this more difficult to diagnose, what do you use to track this? BT OBD II adapter and torque app?

Any ideas?

Thank you

 

[Monk]

I'll run though some basics..... Use your keep it inside(circulation) button, so you're not trying to heat up the outside air(see if that helps). Also don't use the econ mode, to see if that helps. Your fuel mileage seems low over all to me(but I don't know how you drive).
If it's still f'd up look into the threm-stat............ That's about all I can think of........ Good luck.

 

[FG3_drv]

Tried recirculate button, doesn't change anything. Econ is always off, and Im always easy on gas pedal, I noticed that you guys get numbers in 30s no matter how I drive I can't get them. I found that strange, but if tstat was bad all this time I'd get a CEL.

 

[webby]

I looked around and saw 3 other older honda owners having similar issues with cold air blowing while not moving, but warm air while moving. They said "It could be your thermostat, heater core, or sadly even your water pump." All 3 individuals did their thermostat first, and that resolved their issue.

 

[FG3_drv]

I looked around and saw 3 other older honda owners having similar issues with cold air blowing while not moving, but warm air while moving. They said "It could be your thermostat, heater core, or sadly even your water pump." All 3 individuals did their thermostat first, and that resolved their issue.

Yeah I saw those posts, surprising nobody from the 9th gen community experienced this. I'll get tstat and let you know

 

[tacthecat]

Hi everyone,
Weather is getting colder here in the NW (oregon), and I've noticed that I have an issue with my heater. It seems to work fine while i'm moving, blows super hot air when on max setting and I have to turn it down sometimes. However, while standing still or moving less than 20mph it starts to blow cold/tepid air out of the vents on max setting. Engine generally takes about 10-15 or so minutes to warm up while driving. And i've noticed a decline in fuel mileage during this last fuel up, although not significant but noticeable. From 28.9 to 26.2mpg. The latter makes me think t-stat, but due to colder weather and worsening traffic due to holidays I can't tell. Car has 41k and I've had it since september so I don't know what normal is for this car yet, haven't really established a baseline in colder climate. Outside temp in the mornings was around 32 F a few times and generally it stays around 40 F during day. What does not add up for the t-stat failure is that heater works while driving, even on highway. Usually, when t-stat stuck open engine temp decreases and heater starts blowing cold but this is complete opposite. I replaced cabin filter a month or two ago, coolant is at the neck of the radiator (honda blue), 41k on engine, coupe EX. Not having an actual temp gauge makes this more difficult to diagnose, what do you use to track this? BT OBD II adapter and torque app?

Any ideas?

Thank you

Our Si COLD light turns off within a mile and blows warm, not hot within 1 - 2 miles 3 - 4 minutes and hot within 5 miles even when in single digits, would think 1.8L would be similar. If your 10-15 minutes is for the COLD light to extinguish then a stuck thermostat or lack of coolant in engine, (possibly a blown head gasket?) is first suspect - I'd think a bad water pump would trip the HOT light to on or blinking. However if the heater issue "happened" about the same time as the filter change I'd also take a look at the filter and make sure it's installed correctly and not interfering with anything. The decrease in mileage is likely cooler weather/winter gas - we drop off about 10%.

 

[FG3_drv]

Our Si COLD light turns off within a mile and blows warm, not hot within 1 - 2 miles 3 - 4 minutes and hot within 5 miles even when in single digits, would think 1.8L would be similar. If your 10-15 minutes is for the COLD light to extinguish then a stuck thermostat or lack of coolant in engine, (possibly a blown head gasket?) is first suspect - I'd think a bad water pump would trip the HOT light to on or blinking. However if the heater issue "happened" about the same time as the filter change I'd also take a look at the filter and make sure it's installed correctly and not interfering with anything. The decrease in mileage is likely cooler weather/winter gas - we drop off about 10%.

Thank you for input. My cold light does turn off quick (2-3 mins of driving), but heater doesn't start blowing hot until 10 min of driving. Wouldn't a blown head gasket have other symptoms? Like coolant in oil or oil in coolant? Or over pressurized cooling system? Overheating? Misfire due to loss of compression? I ordered a t-stat and gasket, already have a gallon of honda coolant. Although I still don't think it's tstat, I also ordered an OBDII bluetooth adapter. Wanted to get one anyway. I want to monitor coolant temp and see if it fluctuates. I don't suppose I'll get all these things soon due to holiday shipping delays. I have some other upcoming projects too for this car. If anyone wants a diy on asian spec D4s projector headlights, or android navigation let me know I can try to put something together after I have some time to work on my car.

 

[tacthecat]

Thank you for input. My cold light does turn off quick (2-3 mins of driving), but heater doesn't start blowing hot until 10 min of driving. Wouldn't a blown head gasket have other symptoms? Like coolant in oil or oil in coolant? Or over pressurized cooling system? Overheating? Misfire due to loss of compression? I ordered a t-stat and gasket, already have a gallon of honda coolant. Although I still don't think it's tstat, I also ordered an OBDII bluetooth adapter. Wanted to get one anyway. I want to monitor coolant temp and see if it fluctuates. I don't suppose I'll get all these things soon due to holiday shipping delays. I have some other upcoming projects too for this car. If anyone wants a diy on asian spec D4s projector headlights, or android navigation let me know I can try to put something together after I have some time to work on my car.

Cold light going off quickly (at normal time) implies there is coolant around the thermostat and that the thermostat is closed when the engine/coolant is cold. It's unlikely the STOCK thermostat would close normally when cold and then open fully. Are there any indications that the cooling system has ever been opened up or the coolant drained/changed? Is it possible there is an air lock in the heater hose lines - the water pump may not be able to overcome at low engine speed. This happened on our '98 Civic when we had the timing belt replaced, wasn't using the heater at the time but noticed the overflow level dropped. The tech said the refill wasn't done properly and that the heater lines had air in them. After they purged them, I believe by running heater full hot while revving the engine, the coolant level stayed in the normal range.
Anyway let us know what you find out and we can all learn from this forum entry

 

[FG3_drv]

Replaced t-stat yesterday and tried bleeding the system, man I had a hell of a time. It's the only car that's given me this much grief during the coolant bleeding process. I've done so many thermostats and water pumps but this one is definitely one of a kind. Install went smooth, refilled coolant with pentofrost a3. I understand that the car has to be facing an incline, radiator cap should be open, and one must wait until car heats up completely and fans turn on at least twice, then t-stat should open or something. I did just that, except my tstat would not open for an hour or more. It was not overheating, heater was blowing crazy hot air, it was about 50F outside. Anyway it would not open until I got inside and held gas pedal for 3.5 minutes @ 2500 or 3000 rpm. Finally, the bottom hose got super hot. I closed the cap, and called it quits. Every time I drive somewhere I try to check my coolant level and feel the bottom hose. It does not get hot, it was tepid after 30 minute drive yesterday and today I spent 20 minutes driving to work, outside temp was 40F and avg speed was around 35mph. I got to work hose was ice cold.... I dont understand this, very frustrating. Anybody knows the official specs for r18z1 as far as normal coolant temp and coolant bleeding process? I used genuine honda parts (t-stat and gasket).

 

[tacthecat]

Replaced t-stat yesterday and tried bleeding the system, man I had a hell of a time. It's the only car that's given me this much grief during the coolant bleeding process. I've done so many thermostats and water pumps but this one is definitely one of a kind. Install went smooth, refilled coolant with pentofrost a3. I understand that the car has to be facing an incline, radiator cap should be open, and one must wait until car heats up completely and fans turn on at least twice, then t-stat should open or something. I did just that, except my tstat would not open for an hour or more. It was not overheating, heater was blowing crazy hot air, it was about 50F outside. Anyway it would not open until I got inside and held gas pedal for 3.5 minutes @ 2500 or 3000 rpm. Finally, the bottom hose got super hot. I closed the cap, and called it quits. Every time I drive somewhere I try to check my coolant level and feel the bottom hose. It does not get hot, it was tepid after 30 minute drive yesterday and today I spent 20 minutes driving to work, outside temp was 40F and avg speed was around 35mph. I got to work hose was ice cold.... I dont understand this, very frustrating. Anybody knows the official specs for r18z1 as far as normal coolant temp and coolant bleeding process? I used genuine honda parts (t-stat and gasket).

Did the heater blow hot?
You may be chasing a non-issue - If you're not pulling hills or driving in Stop & Go traffic the heater fan seldom comes on in our Si.

 

[FG3_drv]

Yes, I'm starting to realize that. Heater works great. And there must be no air in the system, I tried to bleed it again just in case and tstat opened after 10 minutes of revving at 2500 rpm. I guess I'm just not used to the cooling system on this car.

 

[Darkout]

Sounds normal for a 40 degree day to me, the cold air flow over the motor is probably enough to keep the heat in check.

 

[FG3_drv]

Does anyone know the normal operating coolant temperature limits? I finally got my OBDII scanner and can now see the coolant temp value.

 

[2015Civic.Si]

Hey Guys, sorry to bump a super old thread. I just started having these issues lately and am going to take the car in today to have it looked at (dealership). Did anyone ever diagnose what this could be. Im having identical symptoms, no heat when at a stop. It didnt used to be that way. I own a 4dr 2015 Si and have never had this issue before.