In the temperature-composition diagram of the system 2-butoxyethanol (abbreviated C4E1)/water, SiO2 [mass fraction of SiO2, gamma(SiO2) approximate to 0.01; volume fraction phi(SiO2) approximate to 10(-3)] there exists a flocculation temperature-composition curve running below the binodal curve for x > x(c) (x, mole fraction of C4E1;x(c) = 0.0598). The concentration of the colloidal particles is low enough to consider them an "impurity." In the region of the phase diagram bound by the binodal and the flocculation curve the suspension of the colloidal SiO2 particles is unstable and the particles flocculate reversibly. The difference between the temperature of phase separation and the flocculation temperature increases with increasing values of x - x(c) up to a maximum value of x (x(max)). For x > x(max) the suspensions are unstable at all temperatures studied. For x < x(c) the suspension of the SiO2 particles is stable up to the temperature of phase separation of the C4E1/water mixture. The flocculation curve is assumed to reflect the influence of local concentration fluctuations with long range correlations on the stability of the SiO2 suspensions. For x > x(c) these concentration fluctuations are water rich and interact with the hydrophilic surface of the colloidal SiO2 particles by forming an adsorption layer. This layer is assumed to modify the interparticle potential energy-distance curve and to trigger flocculation. For x < x(c) the concentration fluctuations are C4E1 rich and no adsorption layer is formed at the hydrophilic surface of the colloidal particles.