I have a 98 civic hx manual trans all stock. This problem began last winter and want to try to get it sorted out. The issue is the car never really warms up in cold weather 20's and below and when it does as soon as it idles for more than a few minutes the temperature on the temp gauge starts to drop. Also as the temp drops, the heat in the car starts to feel weak.

Last winter towards the end of the winter the issue started, I replaced the thermostat with one from napa and bleed the coolant ( the thermostat gasket was ripped, letting coolant pass by) and it solved it for a bit and then it came back but the weather got better and the car and temp seem to act normal when its warm out

I have now replaced the thermostat again (oem Honda) old thermostat did not appear to be damaged and bleed the coolant and am having the same issue. I let the car run with the heater on for about 30 min until all bubbles have gone away.

Is there a special bleeding procedure for these this car ( I have bleed systems in the past without issues) ?

Also there are no obvious coolant leaks, every time I check the radiator is full to the brim and the over flow tank is right in the middle region.
Any help is much appreciated, Im sure I could throw some cardboard in front of the radiator or something but I want to try and actually get this sorted out.

 

Describe how you bled the cooling system.

 

After changing thermostat, I opened the radiator and filled it to the top, I then left a funnel stuck in it full of coolant. I then started the car and put the heater on the warmest setting with the fan on high. As the coolant level dropped in the funnel I added coolant until the radiator was full and the level of the coolant had not dropped for about 20 min and no bubbles were present in the funnel. I then put the cap back on and drove the car. After a few days of driving the coolant level has remained the same

 

On the 98 and older civics with the manual slide temperature controls; the slide cable can become too tight and cause the blend door not to fully seal. However this would have no effect on your dash temperature

You can reach under the passengers side behind the cup holder and feel the cable where it connects to the blend door, and push it all the way back

Id suggest running a coolant flush to clean out the heater core if you've already replaced the thermostat. Aftermarket units can fail quickly so I would just replace the thermostat again to be sure

 

I Thanks for the tip on the bend door, I just checked that and it opens and closes all the way smoothly. The new thermostat I put in is oem. I guess Ill have to try flushing out the heater core next.

 

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I am just starting to work on this 2 door HX 2.2, it got flooded out here in Pender county last year hurricane, it also does not get warm I manually opened the valve going thru firewall, disconnected the wire both hoses going thru got warm, so now I guess i start undoing it all below the dash beind the glove box check the core? maybe?

 

The easiest way to flush the core

Disconnect the hoses to the core (use plastic pinch pliers so no coolant leaks out)

buy 3 feet of 5/8 hose and connect to the heater core inlet. Run your garden hose through the 5/8 hose to the core to determine the ease of the flow of water through the core. If there is alot of back pressure and its impossible to easily hold the 5/8 hose to your garden hose without spraying water back at you then the core is clogged

pour a cleaning solution, I use CLR, down the 5/8 hose into the heater core and let soak for an hour

Using pressurized air, blow the CLR out of the heater core. Seal the pressurized air hose into the 5/8 hose so you are blowing maximum air pressure through the core.

If this doesnt work replace the heater core. I have only done the evaporator core but the heater core isnt that much more difficult.

 

 

thanks so much, I pulled thermo, had bad leak motor got real hot I let it cool filled with water it started drove back next morning it would not crank, any thoughts? I hear a clic now under the right side dash when turning the key, I hope I didnt blow the motor, bypassed starter, it just spins, think I burned the starter, hard to get to those hoses I might just take under dash out as the blower is not putting out hard, it was up to just below the dash in flood,
thanks

 

@SenorPescador: A car that went under water in a flood will be nothing but one problem after another. There is a reason why insurance companies always declare a total loss and send them straight to the junkyard. They never try to fix them. Cut your losses now and quit messing with that car.

 

Could be a bad starter. Take the starter out to be tested at ypur local parts store