2000 s10 pickup shows temp gauge at 230 turn heat it blows cold air

How is your coolant level? Heater cores don't work on steam.

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heater core may be clogged, does it go past 230? You can try to flush it out by takeing the heater core hoses off and sending water thru it.

1st try flushing out the entire system....... if that don't work, you'll need a new heater core for sure !

If heater core has become clogged plan on pulling the dash out to replace it .Sounds like a lot of work.Did my heater by myself. There is a U tube video on how to do this.I recommend replacing All the hose's at the same time.S-10 water temp shouldn't go past center of Gage about 210 degrees. With water getting to 230 degrees that means thermostat is not fully open. Change it ASAP. . ,

I agree with the last person. 230 is too hot. Mine runs just below 210 just about all the time. Thermostat or restriction in flow. That dexcool tends to plug thing up. I would try flushing the system and see how much crap comes out. I would wait on replacing thermostat untill you know coolant is clean so you dont plug new thermostat