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Q: car going hot then cold back to hot then cold again

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the car is going set temp to hot then cold then hot again and then cold and stay there and then move up to hot when the car is not moving

My car has 234344 miles.
My car has an automatic transmission.

The information given is not enough to definitively say what the issue is. Consider the following questions. Is it the dashboard temperature gauge that is reading like this, or have you checked the actual engine temp with an infrared thermometer, and know for a fact the engine is jumping temperatures? The dashboard’s gauge may be giving you false information. If not, and the engine is truly jumping up an down, you need to have your vehicle inspected by a technician right away. The gauge however, can be getting false information from the computer, or may just be broken itself. Instrument clusters can vary in price and complexity depending on your make and model. You may want to have your vehicle assessed with a scan tool, to get a better idea if any sensors have failed or are reading strangely.

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