I have a Universal 5411 (M-15) in my 1983 E28+ with the factory modification for fresh waater cooling. Also there is the original Raritan 6 gallon water heater in the mix. The (vertical) heat exchanger has a radiator cap on it. The Raritan has a square metal tank as part of the circuit with a radiator cap on it also. Both of these are connected to the save collant recovery tank. Can anyone with this arrangement please tell me what size (PSI) radiator caps you are using? Thanks.