Originally Posted by blkwgn
Theoretically if both caps are the same pressure they will both vent at the same time. Will this cause air in the system? It should not since they are both venting but as the system cools and excess has been vented will the remaining space create air and not be sucked out of the rad resivior fast enough? or since the resiviour cap is at a higher point in the system will it be cheated the ability to properly discharge?
Typically the answer for the higher PSI caps for the WRX was no, due to the radiator being the weak link. And the reason ppl. went with all aluminum radiators & silicone hoses, then you could run the higher PSI caps.
If you look at your overflow reseviour, the return tube outlet is fully submerged at the bottom of the tank, so when the system "contracts" durning cool down, it will draw back from the bottom of the overflow tank.