Density measurements are reported for 1-methyl-3-ethylimidazolium chloride + AlCl3 binary melts and for 1-methyl-3-ethylimidazolium chloride + AlCl3 + MX ternary melts, where M = Li, Na, X, Rb, or Cs and X = Cl, Br, or I in the temperature range 15-105 degrees C. From these measurements molar volumes and thermal expansion coefficients were calculated. The behavior of these properties is explained by the formation of complex tetrachloro- and heptachloroaluminates in these ionic liquids and by the radii of the alkali-metal cations and halide anions. The binary and ternary melts mix ideally with respect to volume. The effective ionic radius of the 1-methyl-3-ethylimidazolium cation increases with the molar fraction of AlCl3 in the binary melt.