after all this talk about t stats and radiators and having much of the same problems and symptoms that we all are having i went ahead and ordered a new t stat from the toyota dealer today. i had to think long and hard about this and i remember putting in an aftermarket t stat a long time ago like 7 years.but i didnt drive this van cuz it was under construction so i put a new aftermarket t stat in it like feb and still the same symptoms continued to this day.and my previous van had a toyota t stat in it that opperated perfectly normal with no problems. so long story short i,m guessing in the case of t stats ya gotta use original equipment .i,m sorry for jumping in on this thread but, i had to let you guys know i have many of the same situations that you do and i will report back back my findings after i put the new one in! i just gotta make some time(thankfully i,ve been real busy with the carpenter work these days.