1.1 vs 1.3 Radiator Cap

[Seattle944t]

Originally Posted by Suberman

Raising the pressure capability of the cooling system won't strain anything unless and until the cooling system actually reaches that pressure. Adding a 1.3 Bar radiator cap will not change the actual pressure of the coolant until it gets hotter than the designed for temperature it reaches at 1.1 Bar.

That pressure number is the release pressure, not the pressure exerted by the cap. That 1.3 Bar is a maximum pressure before release of coolant. The pressure is exerted by the cooling system which, because the volume of the cooling system is fixed, depends entirely on the actual operating temperature.

Bottom line: changing the radiator cap won't change anything or Toyota would have fit the stronger cap in the first place.

This is mostly wrong. The stock system does exceed 1.1 bar of pressure, that is why there is an expansion tank and you can view changes in the volume of coolant in the tank at normal running temps. If the system didn't exceed 1.1 bar there would be zero reason for the expansion tank because its the expansion that is raising the pressure.

The 1.3 bar cap will raise the pressure by containing more coolant in the system and releasing less into the expansion tank.

Subaru didn't fit a 1.3 bar cap because a 1.1 bar gives plenty of boil over protection for a street driven car and its a standard part for all their other cars. If you live in an area that doesn't see temps much below freezing and want to run a 70/30 water/coolant mix a 1.3 bar cap is probably a good idea. It's certainly a lot cheaper than a complete radiator upgrade.