I've heard of this before but this does not make sense and is analogous to running the radiator fan slower so the air has more time to make contact with the radiator fins. The heat flow equations show opposite since heat removal is proportional for flow rate.
I agree, I have heard this statement made many time, but no one has supplied info or data to back it up?
There are some legitimate reasons for using a t'stat in some cars and situations, and for NOT using one in other circustances.
First of all, a TR will NOT overheat w/o a t'stat if the cooling system is in good shape.
Second, more flow will keep the "hot spots" in the heads cooler, not hotter. Yes, I have data to back this up.
Most racers, at least here in the West, do not run a t'stat. Hard to do a quick cool down when using one.
Most late models cars will run like crap on the street w/o one as it will most likely never go into closed loop mode, or totally screw with the computer.
Bottom line in the original post, doubt that you have a bad t'stat because if it will not open, you will do much more than just run hot, it will boil over. So just remove it, and still overheating indicates a cooling system problem somewhere else.