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Q: only heast when driving cold when idle. heating core flushed twice. heat control valve and blend door seem to be working

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heat when drivig cold when idling. heater core flushed twice. temperature when driving 140-150 degrees then as idle it slowly goes down to blow cold air. heater control valve and blend door seem to be working

My car has 93500 miles.
My car has an automatic transmission.

The normal operating temperature for most automobile engines, including yours of course, is in a range of 185 to 220 degrees Fahrenheit. If your dash gauge is reporting a temperature as low as 140 degrees F, that likely means the car’s cooling system thermostat is stuck in the wide open position, thus preventing the engine from maintaining the desired temperature range. Not only will such cause very low temperature cabin heat but your fuel economy will be lower as well because the engine operates less efficiently if outside the design temperature range. As far as heater cores and radiators, if they are truly plugged, flushing is effective to varying degrees but, of course, just because you go through the "exercise" of flushing doesn’t mean the flushing has succeeded. Technically, you can flow test these parts after you have attempted to unplug them, but it is often more cost effective and more reliable to just simply change out the "damaged" component. Once a radiator is plugged up, it is usually has other problems as well. In fact, if you are really successful in flushing a radiator, you may dislodge the contaminants that are preventing it from leaking. At any rate, in your circumstance the best thing for you is to schedule a thermostat inspection/replacement during which the responding certified mechanic will go over everything and be sure that you do not have additional issues that are a cause of the no heat condition.

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