Car is under a year old, so should be - but don't want to knacker the engine - eek!
I'm scared now
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The radiator cap acts as more than just a "lid" for your radiator; it keeps your engine cool by sealing and pressurizing the coolant inside it. As the coolant in the cooling system heat up, it expands. As it expands it creates pressure in the cooling system. As the pressure increases, the boiling point of the coolant increases. The radiator cap is a pressure relief valve that controls the amount of pressure in the cooling system. What makes this important is that the higher the temperature of the coolant is, the greater the temperature gap between it and the air temperature is. So a cooling system under a predetermined amount of pressure takes heat away from the engine faster, which makes it more efficient.
This pressure increase can raise the boiling point of the coolant by about 50 degrees. The hotter the coolant is, the faster the heat in it moves to the radiator and the air passing by. When the cooling system pressure reaches about 15 psi, the valve in the radiator cap opens allowing the coolant to leave the cooling system. The coolant flows from the radiator to the bottom of the overflow tank through the overflow tube.
the system should easily be able to handle 4 psi and as its a TRD part done specifically for the model then i would put my faith in their research
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COOL...
Now have a sit down Austin :duh: :P