240D coolant amount

[fruitcakesa]

I drained my rad and block, flushed things till clear h2o ran out, replaced the thermostat {the old one was in pieces!}, and the heater control valve which was leaking. Then closed everything back up.
I put in 1gal of MB coolant and 1 gal of h20 which topped the rad to the neck.
Drove around till the t gauge was up to about 90C and had good heat blowing out. I stopped and was able to squeeze in another qt and then drove it around again.
Stopped and added another 1/2 qt but that is as much as it will take. The manual says 11.6 qts but there is no way I am going to get another 2 qts in.
Did I not drain it completely? The car was level when I did it.
I doubt there would be an air pocket someplace or it wouldn't warmup or have heat, right?
The radiator looks clean looking down thre filler neck with no corrosion or scale visible.
Any suggestions?