^^Two radiator caps?? Where's the 2nd one located?

IINM, the reservoir cap is also pressurized on newer Z models. I think 2012+ model years.

I think you're right! Very strange. What benefit would there be to having a separate cap for the overflow tank in addition to the radiator cap? My MY2012 G only has one radiator cap, at the radiator itself. Reservoir uses a traditional screw on cap.

Looking at the 2015 owner's manual, found this pic. Look at part #3 & 12.

http://i.imgur.com/P1V1pLE.png

Google to the rescue!

http://cdn.carwitter.netdna-cdn.com/...-carwitter.jpg

My guess is that it is a pollution control to lessen amount of coolant discharged. I don't see where a two pressure-cap system would do any better at cooling than one and it costs more. But that's just a guess.

Since the OP has a 2012 & mine is the same, I just passed on what mine has. :tup:

Sorry for the confusion...

One cap is actually a non relief cap (the one on the coolant pipe), the other is the traditional relief cap (on the reservoir). Basically it is now like a lot of euro and some American cars where the reservoir is actually a functioning pressurized part of the cooling system and not just an overflow. Do not mix these caps up, they even state which is which in them.