Looking for some advice. My '92 6 cylinder (140K miles) has started overheating. Here's what I've done so far, 2 new thermostats (put in the first one, it still overheated, so I bought a new one and tested that one and it opened at around 200 degrees). Put in the second one and it still over heated. I then replaced the lower and upper radiator hoses. I also removed the heater hoses and flushed it in both directions making sure I was getting a nice clean flow. I get hot air from the heater and it still overheats. When the gage got up to about 250 degrees and was climbing I turned it off and the boiling antifreeze overflowed the overflow tank so I'm pretty sure the temperature gage/sensor is acurate. The last thing I tried was I completely removed the thermostat and it does NOT overheat (and in doing so I also have no heat, which won't work for my nice cold upcoming Michigan winter.)
Any ideas... suggestions?