My Deauville has a pressurized overflow tank, so it seems correct to have two pressure caps. It's an odd system; the lower cooling tube/hose to the rad is directly connected to the tank while the rad is connected to the tank through its pressure cap overflow.
My tank was always empty too, that's because the tank is smaller than complete system volume differential. I have changed my system; plugged the lower connection and made the tank unpressurized (connected only by radcap overflow), but I haven't found a tank to fit yet (ie big enough).
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