I drive a 2004 Honda Civic with a 1.7L 4 cylinder engine, paired to a 4 speed automatic transmission. The vehicle has about 210,00 miles (339,000 kms) with the original engine and transmission. Just ran into a problem last night, I have found that the car does not blow hot air unless I am driving above a certain speed (about 50 km/h). I do not have the AC compressor hooked up anymore as the bearings was going in the AC clutch. So, I had a short belt put on to bypass the AC. With that said, the AC button is off and the car's heat is turned to the max. I tired starting the car from a cold start, opening the rad cap and reving it up to see if there was a possible head gasket leak. No coolant shot out, but I smell some exhaust from the rad cap. Not sure if it is really coming from there as I have an untrained nose. I did make sure to check that it the coolant was full and it is. The thermostat was changed about 2 months ago as the car did over heat in the city for a day. No leaks are visible where I park and the car has not had any over heating issues since the thermostat replacement.
Thank you for the help in advance!
Do you mean the heater for inside the car if so at 50 the inrush of air will sort of come through the vents any way can you hear the motor ac only blowes cold air your heater matrix makes the hot air theres a small radiator type thing behind yhe dash there will be a motor which blowes against the heater matrix making hot air blow there will be mixer valves which mix hot and cooler engine colant which is how you get cooler air blowing it sounds like the heater motor has gone depending on where it isbthe motors are not that expensive and not hard to fit usually avfew screws and clips
@ivanhoo
It has no issue blowing air into the car, the fan still blows full blast. It is just the fact that the air it blows is often cold when at idle. Then once I get moving it works above that speed. Still think it could be the blower fan?
@ivanhoo
Are you adding addition fluid over time I know the car holds 1.3 gal and if low the heater will not work
- No such thing as the heater core mixing hotter and cooler engine coolant. All the coolant in the heater core is the same temperature as the coolant in the engine.
- Air conditioners work their magic by removing moisture from air. That's why you will see water dripping from a vehicle or a window a/c unit when the system is operating properly. A malfunctioning system will actually cause that water to freeze in the a/c evaporator core the is in the dash close to, but not physically interconnected to the heater core. An insect nest in the HVAC drain tube will cause that "a/c" produced water to flood the vehicle floor.
- "Blend doors" direct air flow throughout the HVAC passageways.
- HVAC blower moves air, it has NO effect on the temperature of the air it moves.
- It's possible the engine radiator fan is running all the time, instead of cycling on/off. That will overcool the engine coolant at idle and low speed. Typical cause is a failed "fan control relay".
- A new thermostat failing, as in being stuck partially and not keeping coolant to proper temperature is very possible. "Stant" is the best brand.
- Radiator cap holds cooling system pressure. Typically no or low pressure---poor heat.
- You said, "the car did over heat in the city for a day" and "I smell some exhaust from the rad cap". Honda engines don't tolerate being overheated...head gasket will fail and head can warp. "Combustion leak detector" kit will quickly show head gasket leak/warped or cracked head.
- Flush the heater core by removing the heater hoses, in the engine bay next to the firewall, apply garden hose water to one and catch the water exiting the other. Then reverse the hoses and flush again...you're not done until you get clean water exiting. Over the years sediment builds up in the heater core.
- Water pump. At this many miles, if never changed, it's past due.
