Almost certainly the pump is missing a few blades or the thermostat is not opening. Theres a section on overhauling the cooling system on my web page

If youve done more than 50k miles change both

Mad Mole
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2L Zetec, Cams, Stage 2 head, Valve work, Powerflow, Unichip, AEM Ram, K&N, Ecotek, 75mm Lower etc.
192 BHP, Faster than a speeding Duratec!