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      01-30-2013, 06:03 PM   #21
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Drives: BMW F11 535i Touring
Join Date: Mar 2007
Location: Scotland, Highland Region

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Originally Posted by superflyguy9 View Post
Ahaaaa....didnt realise the EGR stat was two stage hence my confusion thanks Pete. So how do the gearbox stats interfere with all this....are they too set at 88 degrees hence if they fail it gives similar symptoms to a failed EGR stat? Just trying to figure out exactly what is wrong with mine. Now on second EGR stat and already replaced main stat - will give it a proper run tomorrow but early signs are again similar - rockets up to 50 degrees then struggles up to 75, then seems to go up and down from there but never getting past 80
Two stages, but either element can start to fail in the open position, this allows the short circuit of coolant from the radiator and into the coolant flow. Problem is if they fail, flow can start from ambient temperature so very long warm up and if opening completely at a low temperature enough coolant flow to prevent normal ECT. Even from a a gravity feed, there can be a flow of at least 3-litres a minute, through a partially open EGR thermostat. That is a lot of heat loss, particularly from low ambient temperatures.

From a couple of EGR thermostats I 'dissected'.

NOTE: A faulty auto gearbox oil cooler thermostat can do the same, it also can by-pass the main thermostat, and allows cold coolant directly from the bottom of the radiator into the circulating flow.

Oil cooler thermostat is part of the heat exchanger, so a costly repair.


Last edited by HighlandPete; 01-30-2013 at 06:40 PM.