96 Chevy Blazer - replaced thermostat, still no heat

My 96 Blazer wasn't kicking out any heat, so I replaced the thermostat earlier in the week and heat started coming out again. Now, when the temp gauge gets near the red line (which never used to happen), the heat turns
cold, and I have to turn the heat on full blast for the gauge to come back down and the heat to start again. Drove it last night and had no heat at all, although the temp gauge was fine throughout. Coolant is full, but something is obviously wrong. Ideas?
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At this point I would back flush the system to try to clean out the heater core. If that doesn't fix it , i would probalby assume that the core is toast. Good luck. On Thu, 2 Nov 2006 07:02:16 -0600, "blahblahblah"

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You have air trapped in the system. Or, the new thermostat does not have a small notch or hole to let trapped air pass. Look at the old thermostat to see what I'm talking about. My first guess is you just left some air trapped in the system.
Al
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blahblahblah wrote:

Air.
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Paul wrote:

Yes, an air bubble in the engine cooling system.
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