Even a small hole will let some coolant threw. What I've seen is more fluctuation on a drilled thermostat.

well i only drilled a small hole and I did it per recomendation from this site, I thought Bill Boost but cant remember.....i just never remember it running this hot but we broke a 3 yr record for heat today...

when the fins get clogged with stuff it acts like this, and its not real easy to see or fix. you got to take the fans out and back flush the rad fins with the hose, soak it with simple green and flush it again. last time i did that to my bonnie a bunch of pollen came out. there was enough in there it was acting like yours. you should be able to see light from a shop light shine through once your done

Ya, what he said. The problem seems to be lack of air flow.

humm well you can see right thru mine ???

I just went back out and flushed it with hi pressure water and air, its fine and clear....

i have seen the very odd cases were the fins of the water pump were actually starting to wear down and loses cooling efficiency. but that doesnt seem common

i wouldnt worry about it. i made a thread on the same exact subject when io first came to memphis a few mths ago. i think its just our cars. it was only like 80 in memphis that day.