Big hemi specific deal here.

I've found elec water pumps will flow enough at idle and low speeds to cool well if the rest of the system is ok. Get on the fwy and at higher speeds the flow rate v heat being produced ratio changes....then temps change.Get off the fwy at lower rpm, temps drop 25 degrees in 45 secs.

You get to the point where sustained heat created by higher rpm overwhelms the pumps ability to flow at higher speeds, even if the all available air at speed gets through the core. Mech pumps would be different. Ambient temps play a role here too.

Having said that, I dont get over 205 max in the heat in sustained hwy runs. On the street/traffic light stop n go....185deg.

Just what I've come across with a big hemi in an A body.