my drill gets super hot really fast, even just drilling wood, is that normal?

Diagnosis

Rapid overheating during light-duty tasks like drilling wood is a clear sign of mechanical inefficiency or electrical resistance in the Milwaukee M18 FUEL 2904-20. Under normal operation, the brushless motor should remain cool or slightly warm during wood applications. If the tool becomes hot to the touch within minutes of light use, you are likely dealing with "mechanical drag." This occurs when the internal friction exceeds the motor's ability to dissipate heat, forcing the electronics to pull more current to maintain RPMs, which in turn generates more heat in a destructive feedback loop. The root cause is typically found in one of two places: the planetary gear assembly or the motor bearings. If the heat is concentrated at the front of the tool (near the chuck), the grease in the gearbox has likely broken down, leaked, or become contaminated with sawdust, causing metal-on-metal friction. If the heat is radiating from the rear of the motor housing, the bearings are failing or the motor windings are experiencing a partial short, which causes the tool to work significantly harder than necessary to rotate the spindle.

How to Fix It

To resolve this, you must first isolate the heat source and then perform the necessary mechanical service. Follow these steps:

1. Perform a No-Load Heat Test: Remove the battery and any bits. Reinsert the battery and run the drill on speed setting 1 (low) for 60 seconds without drilling anything. Immediately touch the gear housing (front) and the motor vents (rear).
2. Inspect the Gearbox: If the front housing is hot, remove the 4-6 housing screws to open the casing. Inspect the planetary gears for "pitting" or metal shavings. If the grease looks translucent or black, it has failed.
3. Degrease and Relubricate: Use a solvent to clean out the old, contaminated grease from the gear teeth. Apply a high-pressure, lithium-based synthetic grease (specifically designed for high-torque power tools). Ensure the gears are fully coated but do not overfill the housing, as this can cause hydraulic drag and increase heat.
4. Check the Chuck Alignment: Ensure the chuck is not binding. Rotate the chuck by hand; if you feel a "catch" or a gritty sensation, the spindle bearing is worn and the entire gear assembly must be replaced.
5. Clear the Airflow: Use compressed air to blow out the motor vents and the internal cooling fan. Dust buildup in the brushless motor housing prevents the heat sinks from dissipating thermal energy.

If That Didn't Work

• Replace the Gear Assembly: If you find metal flakes in the grease or a chipped tooth on the planetary gear, no amount of lubrication will fix the problem. You will need to replace the entire gear head assembly to eliminate the mechanical drag.
• Inspect the Battery Terminals: A loose or corroded battery contact can cause high electrical resistance, which manifests as heat at the base of the tool. Clean the terminals on both the M18 battery and the drill handle using a cotton swab and 90% isopropyl alcohol.
• Test with a Different Battery: A cell with high internal resistance in an older M18 pack can cause the tool to overheat due to voltage sag. Swap to a fresh, fully charged High Output battery to see if the heat persists.
• Motor Controller Failure: If the motor is overheating despite no mechanical drag, the MOSFETs on the electronic control board may be failing, causing the motor to run "out of phase." This requires a professional replacement of the electronic trigger and control module.

Heads Up

• Avoid "Trigger Feathering": Constantly pulsing the trigger during heavy loads creates heat spikes in the brushless controller; use a steady application of pressure.
• Bit Selection: Ensure you are using sharp, high-quality bits. Dull bits increase the torque requirement, which forces the motor to draw more amps and generate heat.
• Temperature Thresholds: The 2904-20 has built-in thermal protection. If the tool shuts off completely, do not attempt to restart it immediately. Let it cool for 15 minutes to avoid permanent damage to the motor windings.
• Storage: Never store your drill in a sealed plastic bin in direct sunlight or a hot vehicle, as this degrades the gear grease and the battery chemistry over time.