I have done some searching during the last week and found some good info. What i am wondering is when the heater doesn't work it would be the heater core line being plugged in most cases. My car has heat but only on low fan speeds. I assume the line may be getting plugged but has some flow right now. Does anyone know where the blockage is usually at? I have seen where the core was replaced but it still didn't fix the problem. I read about unhooking the hoses going into the fire wall but do you run more than water through it?

 

The heater core itself plugs up with gunk. Pull the hoses off at the front of the engine, not at the fire wall, apply pressure with a garden hose on one line, and hope it starts to flow out the other line. Do NOT let any water get on the Opti.

 

yea flushing with a garden hose works really good, just make sure to flush it in the opposite direction as the water pump normally flows our you might not get everything out. Flush it both ways a couple times... you wont believe the amount of heat once your done!