For the typical EJ255 engine in the 818, what is a good coolant expansion tank size. I would like to replace the subaru plastic bottle with something that looks better. wondering if the system with more coolant would expand more than on the WRX, and what that translates to in terms of size? I haven't measured the stock plastic bottle but it appears for be around 64 oz? Has anyone tried a smaller bottle, say 20oz, and is it adequate?