Most times overcooling iis due to a bad thermostat.
What happens is the thermostat is not opening properly and lets the coolant stay in the radiator too long and its cooling it too much.
Most cars will not operate properly until they get up to a certain temperature and they will have a lack of power.
Another possibility could be with the cooling fan(s).
Modern cooling fans work off a thermo contact switch.
The switch can be telling the fans that the coolant is at the right temperature causing the fans to not stay on long enough.
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