quote:Wouldn't the amount also depend on the radiator volume?
Yes, but probably not more than about a quart.
quote:When I changed my radiator (copper/brass) the system used about 4-1/2 gallons.
That sounds about right, especially if the engine block wasn't drained. That's why I said "bone dry".
I've amended the quantity (slightly) in the above post due to my error.
John