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Someone has either reversed the wires on the temperature gauge or damaged the wires from the engine to the gauge and spliced them back backwards. It is a simple reverse of polarity.

First, check your thermostat, your car may actually be overheating slightly due to the thermostat sticking. If it sticks then no anti-freeze flows through the heater core(providing the cab with heat), which will cause overheating. If it eventually opens, allowing flow, and cooling off the fluid/engine (gauge drops) then fluid flows again giving you anti-freeze through the heater core and heat pours out. Check it by removing it and putting it in a pan of water and boiling the water with a thermometer in the pan (try to hold them both off the pan surface with tongs, it may screw up your reading), watch close for the temp at which it opens, should be 180F, but check for your car.

Second step would be to check your water pump, low flow from a water pump could also cause the same problems.

After those two, "you're on your own kid"

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โˆ™ 2015-07-17 17:29:59
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Q: Why would a car heater blow hot when the gauge reads cold and vice-versa?
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