Possible Causes:
* Faulty Fuel Level Sending Unit: This is the most common cause. The float inside the unit may be broken, the potentiometer (variable resistor) may be failing, or the connections may be corroded. The spinning gauge suggests a complete failure of the unit's ability to accurately report the fuel level.
* Wiring Issues: A break, short, or corrosion in the wiring between the sending unit and the instrument cluster could cause erratic behavior. This is less likely to cause a full 360-degree sweep but is worth checking.
* Instrument Cluster Problem: While less likely given the 360-degree sweep, a faulty gauge in the instrument cluster itself could be the issue. This is usually diagnosed by checking the gauge with a known good sending unit.
Repair Process:
This is a job best left to someone with mechanical experience, especially given the need to work with fuel. Safety is paramount. Gasoline is highly flammable. Always work in a well-ventilated area, and disconnect the battery's negative terminal before starting.
1. Safety First: Disconnect the negative battery terminal. Allow several minutes for the car's electrical system to fully discharge.
2. Locate the Fuel Tank Sending Unit: This is usually located at the top of the fuel tank, often accessed through a hatch under the rear seat (check your repair manual for your specific model). Some models may require dropping the fuel tank.
3. Drain the Fuel Tank (Partially): Siphon or pump out a significant portion of the fuel to reduce the amount you need to work around. This makes the job much safer and easier.
4. Drop the Fuel Tank (If Necessary): This often involves disconnecting fuel lines, electrical connectors, and support straps. Consult a repair manual for specific instructions.
5. Access and Remove the Sending Unit: Once the tank is accessible, carefully disconnect the electrical connector and fuel lines from the sending unit. Unscrew or unclip the unit from the fuel tank.
6. Inspect the Sending Unit: Carefully examine the float, arm, and the potentiometer. Look for cracks, breaks, corrosion, or any sign of damage.
7. Repair or Replace the Sending Unit: If the potentiometer is broken, the unit likely needs replacing. Replacing the whole unit is usually easier and more reliable than trying to repair the internal components.
8. Reassemble Everything: Reinstall the sending unit, reconnect the fuel lines and electrical connectors, raise the fuel tank (if applicable), reconnect the fuel lines, and secure everything.
9. Refill the Fuel Tank: Carefully fill the tank to the appropriate level.
10. Reconnect the Battery: Reconnect the negative battery terminal.
11. Test the Gauge: Check the fuel gauge to see if it operates correctly.
Important Considerations:
* Repair Manual: Obtain a repair manual specific to your 1998 Chevy Malibu. This will provide detailed instructions and diagrams.
* Tools: You'll need various tools including sockets, wrenches, screwdrivers, a fuel siphon or pump, and potentially jack stands.
* Professional Help: If you're not comfortable working with fuel lines and car repairs, take your vehicle to a qualified mechanic. This is a job that can be dangerous if not done correctly.
The spinning gauge is a clear indication of a problem that requires attention. Don't drive the car until it's fixed, as an inaccurate fuel gauge could lead to running out of gas.
