It appears that if you want to use this particular solution of nanofluid in
a high flow situation, you need to cut it with distilled water. Without
knowing the percent volume of the nanoparticles in the solution, it seems
that there is too high of a concentration of nanoparticles, making the
solution too viscous.

Low flow - thermal conductivity of fluid matters alot

High flow - high viscousity reduces turbulence. The negative effect of that
to heat transfer outweighs the positive effect of higher thermal
conductivity

Depending on the flow, there is an optimal concentration for the
nanoparticles.