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Discussion Starter #1 (Edited)
I was replacing my expansion tank, the bottom fitting where the tank clips on has a spring loaded check valve. Circled in the picture is how it is supposed to look. Mine was cracked and spring and plunger where loose. What is the actual fitting the expansion tank is connection to? It is not the radiator, the best guess it has to something with the Tranny cooler. I cannot find the actual part that this check valve resides in. Anyone??

I had to put it back together with out the check valve.
 

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That's the thermostat for the transmission cooler. These often crack and need replacement with the expansion tank. Their role is to allow the transmission to warm faster in cold weather. Here's a diagram that illustrates. This thermostat is item #4. GL

P.S. In my opinion, you're should be okay without during summer but replace before cold weather. And if mucking around down there, replace orings including where tran cooler mounts seals to the radiator, item #3.
 
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