To　solve　the　problem　of　braking　torque　decline　or　even　brake　failure　of　vehicle　retarders　caused　by　high　temperature　due　to　long-time　or　high-power　braking,　the　nanofluid　with　high　thermal　conductivity　is　introduced　into　the　previously　proposed　novel　retarder.　To　evaluate　the　nanofluid　cooling　capabilities,　a　model　depicting　the　vertical　fluid　flow　in　the　retarder　is　formulated.　Adopting　similarity　transformations　and　a　shooting　method　coupled　with　Runge–Kutta　iterative　technology,　the　model　boundary　value　problem　is　tackled　numerically.　The　cooling　capabilities　of　three　typical　ethylene　glycol　(EG)-based　nanofluids:　Cu–EG,　Al2O3–EG,　and　TiO2–EG　are　investigated　and　compared.　Finally,　an　experimental　test　is　carried　out　to　examine　the　temperature　rise　and　the　variation　of　braking　torque　for　the　retarder.　It　is　demonstrated　that　Al2O3–EG　nanofluid　has　the　highest　Nusselt　number　(rate　of　heat　transfer),　and　more　importantly,　the　braking　torque　of　the　proposed　retarder　decreases　by　only　8.2%　under　high-power　braking　condition.　©　2021　Wiley　Periodicals　LLC