There are two things I have read on Blatchat at regular intervals over the last two years. Drilling holes in thermostats and blanking off areas of radiator
I'm my opinion both actions are fundementally wrong.
The thermostat is fitted to prevent the majority of engine coolant passing through the rad until the specified working temperature is reached. Typically 80 deg C. If working properly, it will then open allowing coolant in to the radiator. If driven hard it will fully open, if the rad can't keep up with the amount of heat produced then fan will start.
So if the stat is working there is no point in blanking part of the rad area as if working temp has not been reached the rad is largely switched off.
Equally, if the stat is working, drilling extra/ larger holes in it will only have the effect of slowing the rise to working temp, or worse prevent it from being reached at all.
I suspect that many cases of engine temp problems are associated with failed, or partially failed stats. They can have quite short lives. But I can't see any circumstances where drilling the stat or blanking the rad is the right thing to do.
Having said all that, air locks really must be avoided as this results in localised hot spots which are the cause of many cylinder head problems.
Peter