Don, yet another possibility, although IIRC it's the non-heat-sinked components that are getting hot that are the concern.
According to the i-MiEV Owner's Manual, the car uses "Dia Queen Super Long Life Coolant Premium", or an equivalent "high quality ethylene glycol based non-silicate, non-amine, non-nitrate, and non-borate coolant with long life hybrid organic acid technology". I've used the manual maintenance schedule to point out that only at 240 months (20 years!) does the manual specify to change the motor coolant and heater fluid.
Our i-MiEV cooling system does not undergo the dramatic temperature excursions to which an ICE vehicle is subjected, and thus perhaps is not subject to the same issues. If anyone does change the fluid, it would be nice if you could do a before/after thermal measurement.
EVs: Two '12 Wht/Blu SE Prem., '13 TeslaMS85, three 156v CorbinSparrowsLi(NMC), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab96
Hybrids: 48v1kW bike
Mothballed ICE: Orig.Owner '67 Saab96V4, '88 IsuzuTrooper; '76 MBZ L206D RHD RV