dont the Kenlowe cool it?
maybe if the Kenlowe only cuts in when the temp gets in the red - yu need to consider repositioning the thermo switch - as per previous discussions - unless yu can alter the switching temp - in whuch case turn it down a notch.
impellers can become loose - but its very uncommon.
One of the tricks used to clear crud out of the cooling system is to put in a dose of dishwasher liquid (gotta be liquid, not powder) . Yu dont want it in too long, coz its corrosive - but its damn good at clearing out crud and oilly deposits n stuff - not blockages, but it cleans the system really well.
the fan does cool it and yes i could turn down the "on" temp so it comes on earlier - it's the change in behaviour that's got me stumped
normally if you watched the temp guage it would rise to just past vertical and then settle back to just before vertical - this is as i'd expect ie stat opens when temp gets to whatever (88?) then flows through rad and cools
whereas now (if i'm booting it) it doesnt drop back after passing the vertical and continues to increase untill the kenlowe kicks in
from the sound of it i now think the rad isnt doing what it should do - might have another go at flushing it using your tip