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Q: Fuel gauge will fluctuate from full to empty on half a tank of gas. on 1999 Chevrolet Malibu

Sometimes the orange low-fuel light will come on and sometimes it doesn't. Mileage on half a tank of gas varies from 35-45 miles. Spark plugs & wires & intake manifold gasket were recently replaced. No lights other than the low-fuel light come on. The temperature gauge was going toward hot (about 2 increments past the half-way mark). Pulled car over immediately. Once cool opened the hood and notice coolant under the reservoir tank. Added more coolant & it hasn't ran hot since. Based on the issues mentioned, does it sound like I have something that needs to be diagnosed at a shop.
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No diagnosis is necessary. The fuel gauge sending unit on the side of the fuel pump is failing and causing erratic behavior of the fuel gauge. The sending unit can be replaced or the fuel pump and sending unit together can be replaced. Replacing both will cost slightly more. However, replacing both can save the labor cost of doing the job again to replace a failed fuel pump later. The majority of labor is due to removing and reinstalling the fuel tank to access the fuel pump and sending unit. Regarding a temperature reading two notches above normal, it is not an overheating event. The slightly higher temperature most likely caused more expansion of the engine coolant resulting in a slight loss if the reservoir was very full.
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