[tooski]

Both my 461 and 408 are doing this.

I will ad coolant up to the filler neck, and a pint or so into the overflow reservoir. After driving a couple of hundred miles or so I will check the level. The level will be down to expose 1-2 of the rad tubes. When I refill to the top of the tubes this will occur again. However, if I do nothing and just monitor the level , even after several hundred miles, I have never seen the coolant level lower than 1-2 tubes exposed. On either engine whether the level is full or 1-2 tubes low the coolant temperature is not affected.