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MIL-PRF-87252 covers a hydrolytically stable, dielectric synthetic-hydrocarbon coolant for electronics, radar and avionics. It is a polyalphaolefin (PAO) fluid, NATO code S-1748, for use from −54 °C to 200 °C. The specification sets no density limit. It lists a typical specific gravity of 0.800 at 15.6 °C in Table III, as information only.
The temperature data are the three dilatometer densities printed on the ROYCO 602 data sheet: 0.8058, 0.7392 and 0.6768 g/cm³ at 0, 100 and 190 °C. The AeroShell Fluid 602 listing repeats the same numbers. They are typical values for one product, with no uncertainty stated.
The curve is the exact quadratic through those three points, ρ = 805.80 − 0.65161·T − 1.439e-04·T² kg/m³. It is solid from 0 to 190 °C. Below 0 °C it is an extrapolation of the same quadratic. Coolant systems often run at −40 °C, so expect the real density there to differ a little from the dashed line.
Use density to convert flow rates. A volumetric flow in gal/min times the density gives a mass flow, which you then multiply by the specific heat and the temperature rise to get the heat load. See also viscosity, thermal expansion (how much the fluid grows when it warms) and pipe velocity.