Would think this would be basic stuff but would like to run it past the group. Subaru eg 33 and the radiator is a Caples unit from a serroco that has upper and lower for in and out and a small maybe a quarter inch off one side at the top. Pics to confirm. I purchased an expansion unit that has threaded outlet/inlets near the top and bottom and also an overflow /pressure release under the cap that looks to also be about a quarter inch wide round. Should also mention that the radiator also has a threaded plug on the opposite side of the main inlet/outlet that looks to similar in size to the ones on the expansion tank

So that being said the inlet and outlet are straight forward. I’m guessing now that the bottom of the expansion tank would tie into the plug on the radiator that are both the same size and threaded. The overflow pressure on the expansion tank under the cap will be pressure overflow out the bottom of the car or into a catch can so to speak

Now comes the hard part. What’s that quarter inch outlet on the top of my radiator for and same question about the other threaded hole up on the side of the expansion tank used for??

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The bottom of the exp-tank should tie in to the suction side of the engine. I put an anode in that 1/4" opening. https://www.amazon.com/s?k=radiator+anode&a...rect=mhFallback

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Almost looks like it’s got a built in trans cooler. What’s the radiator for originally?

I have a Scirocco with the same radiator (although stock, not aluminum). The connection on the bottom driver's side with the threaded plug is for the radiator fan switch. On mine, the expansion tank connection is a nipple near the outlet on the top passenger side.

Scirocco