Soldato
I use one of Aqua Computer's pressure relief membranes (as linked to in previous posts) on a couplenof my builds. Both are semi-passive that they aim for quietness as the primary concern and only spin up the fans if/when the temp gets over a certain amount. My everyday machine (link in my sig) only spins up the rad fans when the coolant temp gets over 36°C. That's a potential delta of around 20°C and I've had no issues with the membrane installed. I also have a level sensor on the Res that is pressure based and that requires a pressure relief so that the only pressure is caused by the weight of the column of coolant in the res.
Other manufacturers do a similar product - Barrow, Bitspower etc - haven't tried them but would presume they are fairly similar. Even with the pressure relief, you don't want the coolant to be all the way to the top as the valve will release excess pressure of air. If you have coolant to the top, it will presumably release excess pressure of coolant....or leak.
If you absolutely had to have a completely full res for looks, the answer would be to have an expansion tank elsewhere - a small res in the loop (probably higher up) - that was used to provide that expansion space.
Other manufacturers do a similar product - Barrow, Bitspower etc - haven't tried them but would presume they are fairly similar. Even with the pressure relief, you don't want the coolant to be all the way to the top as the valve will release excess pressure of air. If you have coolant to the top, it will presumably release excess pressure of coolant....or leak.
If you absolutely had to have a completely full res for looks, the answer would be to have an expansion tank elsewhere - a small res in the loop (probably higher up) - that was used to provide that expansion space.