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    Member No: 166993 retnavy is an unknown quantity at this point retnavy's Avatar
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    Cooling system flow problems

    I got an 88 750il a couple months ago and recently have deveolped a cooling flow problem. Thinking waterpump and replaced it. Still no flow after bleeding the system per instructions etc... When I took it apart I found the thermostat removed and the heater core bypassed. One side of the recovery tank "y" hose connected to rear header. I heard that the heatercore and valving MUST be connected??? Is this really true? Thermostat must be installed as well??? Any help would be greatly appreciated!!! Thanks in advance!


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    Cooling system flow problems

    I heard that the heatercore and valving MUST be connected??? Is this really true?

    Heater core can be disconencted. PatrickC750 also did that. It is in any case always disconnected when you close the heater valves. But the recirculation must be ensured when you disconnect the heater core.


    Thermostat must be installed as well???

    Yes, it is better. The BMW system is layed out in such way, that priority is always on the engine cooling. The engine cooling is the small cyclile, the heating system is the arge cycle. The t-stat opens when a certain temp has been reached, onl;y then will the large cycle be opened.
    Shogun's E32 Tech Tips: http://tridem.han-solo.net/auto/erich/auto.htm

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    Inner Circle ©160 since: Aug 14, 2003 cheung1 is an unknown quantity at this point cheung1's Avatar
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    I am still bypassing the heater core

    Highline is correct: I am still bypassing the leaky heater core and am awaiting some time out in October that I can spend at home doing that replacement plus A/C conversion.
    As for the thermostat, A few years ago I studied the operation of the thermostat I made a note that the thermostat helps direct the flow of coolant into and out of the radiator at the set temperature. I say this because I am not 100% sure. The way I understand the operation is that at operating temperature, the thermostat is like at the intersection of a figure "8". Engine loop on the low side and radiator loop on the high side. If thermostat is missing, then the water pump will push majority of coolant around the engine loop, but no device will direct the hot coolant into the radiator loop. Thus the coolant circulating through the water pump only gets hotter, but movement through radiator stays slow and cold.Patrick C 88 750 159K

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    bravo, nice explanation, Patrick

    some poeple still believe that if they omit the thermostat they get a better cooling. But that is not the case with the BMW system.

    Here a drawing of the coolant circuit of the V12 engine
    http://s71.photobucket.com/albums/i155/shogun_bucket/?action=view&current=coolant_circuitV12.jpg
    click

    BTW, Patrick: did you already buy a new heater core and the plastic pipes from there to the connection at the firewall? Where and how much? We have to change them too on the Alpina B12 "Take" (Mitsu) got 2 weeks ago. Just a slight coolant smell at the moment, no noticeable coolant loss too, but we want to fix it before winter comes.
    Take has done it on his Highline last year, I posted some pics on BB, he says not so difficult, he did it in one week in the evenings, totally 5-7 hours he says. Shogun's E32 Tech Tips: http://tridem.han-solo.net/auto/erich/auto.htm

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    core $169; pipe set $58

    I bought them from autohausaz last December. Also got the square nuts that Take pointed out (thanks!). Highline: From your coolant circuit for V12 diagram it does look like if the thermostat is missing, there is no tendency for the circuit to direct hot coolant into the radiator loop. There must be some posts about not installing thermostat I wonder if in every case the M70 would overheat, or if there is a potential reason why some engine did not overheat?Patrick C 88 750 159K

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    Re: Cooling system flow problems

    Thanks for the info! Got t-stat on order and will update when I get it in and restart the car. Thanks again!!!

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