KidDxbOrI

I have a 93 civic sedan lx heat works for about 40 seconds then slowly turns cold , changed thermostat , water pump , cleaned rad , and flushed water through the heater core , still no heat , can anyone help me out ( also bleed cooling system and topped it off

B16Civic93

have you checked to see if the hoses going to and from the heater core are still hot when the heat starts to fail? I'm thinking it could be the door in the blower box not moving/shutting completely to divert the air across the heater core.

slowcivic2k

The door would have to sag slowly over time to produce the fading heat symptom.

Sounds like there is air in the system. Any modifications to the cooling system?

Did this loss of heat occur suddenly? and if so, when, and what was the last thing done to the car before the heat stopped.

KidDxbOrI

I bought it like that , so. Ever really checked till now , I bleed the cooling system already but it still fades . Both hoses do stay warm though

fcm

the 93 Honda civic uses a water valve, there is no blend-door to direct air away from the heater core, if car has A/C the evaporator is inline with the heater core, for A/C, [or cooler air the water valve is closed, [fully closed for A/C], so not sure what is happening with yours.

Does airflow "slow down"?
Do all 4 blower speeds work?
Does mode control work properly, [can you change from vents/floor/defrost] and stay where set? 94