just got another couple of ideas..1 thermostate sticking[not opening fully]you can use jug of boiling water to check operation,[dont use a plastic container they cool off to quick.] let cool. i use acc temp gauge[capilery type ;not electric] to check temp of water & let cool to about 5deg hotter than stamped on thermostate[water will coll off a bit more when you put it in the water as it will take time to open if it does not fully open replace it.do not cut center out or leave it out they are need to regulate water flow as well as temp..2; cloged rad there is 2 opitions to get cleane 1-preasure back flush 2-remove tanks & have it speared please do not do either of these if you have no experieance get done at rad shop. if it is clutch fan you can repair them if they are screwed together i buy the silicon oil from toyota spare parts them ..[ must use right oil]..normerly 1 bottle is enough on a 4cyl
but depends on size of hub.don't forget to back flush eng....p.s normal gaden hose dose not normaly work to do flushing.