How much does water expand when heated, and does salt affect that?
The volumetric expansion of a liquid is given by the following equation
$$\Delta V=V_0\beta\Delta T$$
where $\beta$ is the coefficient of thermal expansion and $\Delta T$ is the change in temperature.

Here's a link to a nice table containing coefficients of expansion for water, both pure and salinated.  Wikipedia shows the maximum solubility of salt in water to be around 36% (w/w).

From the first link we find that

for pure water at $25\ \mathrm{^\circ C}$: $\beta = 257\times10^{-6}/\mathrm K$

for water with 35% $\ce{NaCl}$ dissolved at $25\ \mathrm{^\circ C}$: $\beta= 297\times10^{-6}/\mathrm K$

Now you should be able to calculate the values you are interested in.