Tiguan leaks when it is cold outside…

Hi,

My 2013 VW Tiguan leaks when the temperature outside gets into the 30’s F.

All summer it is fine, but when winter comes it loses coolant very quickly. Once the engine warms up, it seems to hold coolant.

I replaced the water pump with an aftermarket metal one 5 years ago. Could a failed seal on the water pump only leak in the winter?

I’m going to pressure test it this weekend.

For the last couple years I’ve just added coolant in the winter, but I want to fix it up again.

Thanks!