Silicone organic blends for use as lubricating oils, hydraulic fluids, dielectric fluids, coolants, and in compressor or vacuum pump applications, have improved viscosity stability when the polydispersity of the silicone fluids used in these blends, i.e., their molecular weight distribution (M.sub.w /M.sub.n), exceeds 1.5. The viscosity rise of the silicone organic blend is less than one centistoke (mm.sup.2 /s) when aged 14 days in an oven at 100.degree. C., compared to viscosity rises of about 1.3 to over 3.5 centistokes (mm.sup.2 /s) for commercial silicone organic blends using silicone fluids with polydispersity less than 1.5.