A brief "google" search showed 18 psi for the coolant bottle pressure cap.
I refer to Rock Auto as my technical data source. All the radiator caps they recommend for your car and engine are listed as 16psi rated. The normal range is 14-18psi which makes sense. They are less than $5 each and your local parts person should be able to pick out the right one. They may even install it for you and look things over. But do not open the cap on a warm/hot engine. I hope this helps.
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