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Old 01-13-2011, 12:17 PM   #1
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How does auto trans cooler work?

I've searched to no avail, and am left feeling puzzled. How does the transmission cooler in our E46 automatics work?

What I do know:
There are two lines running from the transmission to the trans cooler/heat exchanger.
The trans cooler has what looks to be inlet and outlet ports that attached to the lower left part of the radiator.
There is an auto trans thermostat at the bottom of where the expansion tank attaches.

What I don't know:
I would think the trans cooler/heat exchanger does the cooling but if so why does it have inlet and outlet ports going into the radiator?
Were does the auto trans thermostat allow/block flow of fluid to? is it coolant or trans fluid it regulates?
Is there space in the radiator that is reserved for the trans fluid?

Thanks guys I can't seem to figure this one out despite looking at numerous photos and parts diagrams.

Last edited by Hector45; 01-13-2011 at 12:22 PM.
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Old 01-13-2011, 12:25 PM   #2
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The cooler is integrated into the radiator. Seperate cooling channels.
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Old 01-13-2011, 04:36 PM   #3
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is it a bad idea to run the car without the whole tranny thermostat? mine broke and i got the entire thing out so its wide open, and i ordered a new one but wont be here for a week, what do you think?
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Old 01-13-2011, 04:45 PM   #4
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It would be best to wait for the new A.T.T. to arrive...
It would NOT be wise to run your vehicle without the trans. thermo.
You would end up with a lot of hot coolant flowing back down to the transmission cooler.
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Old 01-13-2011, 06:56 PM   #5
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This will explain how the transmission cooler works: http://forum.e46fanatics.com/showpos...&postcount=147 . Engine coolant both helps to warm the transmission fluid as well as cool it. This happens outside the radiator in the transmission heat exchanger.

Last edited by Sansho; 01-13-2011 at 06:58 PM.
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Old 01-16-2011, 08:42 PM   #6
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Thanks alot Sansho
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Old 01-16-2011, 08:43 PM   #7
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Some people buy aftermarket trans coolers as well
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