Archived from the Tools In Action forum (Automotive). This thread is read-only.
So I flushed out my heater coil with garden hose full water pressure and everything was working great. I drained and refilled the coolant too. then very little heat,
fan blower is good, Actuator door motor is good. I pinched the bypass hose tight with permanent clamp to force coolant through the coil and more heat but not enough.
What could possibly be clogging the coil? Is there any additive to dissolve clogs?
Welcome to the forum.
In a case like this vehicle identification may be useful.
My speculation is that the coil is not plugged. That is very easy to determine by disconnection of both heater core hoses, then squirting garden hose water into one and observation of good flow out the other.
My speculation is the most likely issue is an air bubble that needs to be “burped”. Many vehicles have a bleed screw on the thermostat housing, to bleed air. That is a great starting point.
The second possibility is that the blend air door isn’t routing cabin air over the heater core.