[cycleguy55]

I'm using a Factory Five inline filler with provision for an overflow tube. It's mounted at the high point of the upper radiator hose.

A small expansion tank is horizontally mounted between the engine and radiator, and is connected to the radiator with heater hose tubing. This has a thermostat neck with an overflow tube as well, and is slightly lower than the inline filler.

Both overflow tubes are connected to a low-mounted tee, then to a plastic coolant recovery reservoir in the driver side wheel well.

I'd like to simplify the system by using a single recovery tube, meaning one of the two pressure caps would have to be replaced with a blanking cap that wouldn't release under pressure.

Question: Which pressure cap s/b replaced by the blanking cap - upper inline or lower? Why?