I have Mike Everson's hard coolant lines with the rad inlet on the top right (passenger's side).

There is that plastic black fill cap overflow coupler with 13240 written upside down.

Does anyone know what type it is? American? European? Japanese?

All I know is that that Behr cap fits.

I'm trying to change the cap as it opens around 22psi (150kpa) and let's a lot of coolant flow into the rad's overflow tank, so the coolant that is in my VW overflow tank located higher is flowing there. If I open up the cap, it will spill cuz there is coolant at a higher level (my engine head sits quite higher too).

I'm trying to know the hole size, probably around 1.5", and what type that coupler is. People selling fill caps often don't know their size, they just know "fits Japanese", "fits American"...

Mike himself doesn't know the size.

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