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Thread: Audi A4 cooling system

  1. #1
    Join Date
    Nov 2011

    Default Audi A4 cooling system

    hi i bught the Audi A4 printed manual for my 2004 A4 Quatro sedan. There is no heat coming from the car heater. the dealer said it was the heating core and it needs replacement at huge cost. Several youtube show how to back flush the heater core...

    ok so i did the heater core back flush and it runs freely and cleanly with fresh water flowing thorugh nicely.
    dealer had replaced the thermostat last spring and that fixed heating.

    the the top return hose from heater core is cold, bottom feed hose of heater is only warm, not hot like the top of the radiator hose, the temp guage is normal on the dash, heat in cabin is at max (note AC works great) and switching AC on off has no effect. The vent control moves the air flow feet, dash, defrost as expected.

    i expect there is another valve, or device between the thurmostate and cabin heater core, what is that the Haynes manual does not show the complete cooling fluid flow and the hoses and connections.. PS tryed to blow the heater return hose with air and i blew back from the heater core sorce hose wired i would have thought it was not isolated. Even if all the fins in the heater core fell off would not the return line from the core be hot? not cold?

    i have had lots of cars which were eventually retired at 250k miles or more and never had heater troubles on any of them.

    is there any electronic control that can be tested? i am completely baffled by this...

  2. #2
    Join Date
    Jan 2007


    The fact that you have verified that water flows freely through the heater core would seem to indicate that it isn't restricted. Strange though, that one hose is warm and the other hose is cold. I think there must be a restriction elsewhere, like in one of the hoses or where they attach to the engine.

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