Just because you've had the system flushed, doesn't mean there isn't a blockage in your heater core.
Your engine has what we call a "reverse flow" coolant system. I won't bore you with the technical details. But what this means is, if your heater core is NOT blocked, and your thermostat is functioning correctly, then you either have a malfunctioning water pump, or you are getting air in your system.
Because you have a reverse flow system, when air gets in the system, it collects inside of the heater core and stops the coolant from flowing through it. (That's how you get your heat) A quick way to check to see if this is the case: When your engine is fully warm, turn on your heater and place the controls on the hottest option with the fan blower on high. Then rev the motor to at least 1500 r.P.M.'S. If the air becomes hot while you are reving the motor, then that's proof air is in the system.
If that doesn't work, then it's probably your water pump. However, if it is you water pump, then your engine should frequently over heat. Which makes me believe it's air in the system.
And unfortunately, if it's air, then that means you have a blown head gasket. (Expensive)
Finally, to check if you have air in the system:
Take off the cap to either the radiator or the surge tank. Look inside while someone revs the motor to at least 1500 r.P.M.'S. If you see air bubbles in the antifreeze, you definitely have air in the system. (Blown head gasket)
Sunday, January 3rd, 2010 AT 10:38 PM