Overheating issue temperature go to 212 then back to 190 then goes up to 248?

2012 DODGE CHARGER
260,000 MILES • 3.6L • V6 • 2WD • AUTOMATIC
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BABY MECHANIC
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Car temperature on digital display on instrument cluster shows coolant temperature goes to 212, then back to 190, then goes up to 248, then back down to about 230. I am able to still drive for about 5 minutes, then temperature red lines. From my understanding the radiator, the water pump, the heater core, the thermostat and housing, the fan, reservoir and cap, and upper radiator hose have all been replaced. Sometimes when the temperature is reading 230-250, I would still have heat but sometimes I don't.
Jan 31, 2023 at 3:03 AM
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STRAILER
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First, I would wait for the engine to cool down completely then open the radiator cap to check the coolant level because this is what the temperature gauge does when the cooling system is low on fluid.

This video will show you how:

https://youtu.be/GSE9skKnOgY

If the coolant level is okay, I would try replacing the engine coolant temperature sensor. Here is the location in the images below. If the car still has the problem, please do a blown head gasket test.

This guide can show you how:

https://www.2carpros.com/articles/head-gasket-blown-test

Check out the images (below). Please let us know what you find. We are interested to see what it is.
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Jan 31, 2023 at 10:05 AM
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BABY MECHANIC
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Okay, thanks. I will try the block test and I have already replaced the sensor but was still having an overheating issue. Oh yes when I first started looking at the overheating issue the coolant would boil in the reservoir when it stopped the reservoir would be full then a couple minutes after that you would see the reservoir go all the way down.
Jan 31, 2023 at 10:32 AM
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STRAILER
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Yep, it sounds like a blown head gasket, please let me know.
Feb 2, 2023 at 12:23 PM