What Happens if Oil Gets on Alternator: 3 Vital Tips to Know


Oil on an alternator can lead to insulation breakdown, increased electrical resistance, and overheating. It compromises the alternator’s efficiency, potentially decreasing output by up to 30%. This contamination accelerates wear on bearings and brushes, potentially reducing the alternator lifespan by 25%. Immediate effects include voltage fluctuations and potential alternator failure, requiring urgent cleaning or replacement to prevent further electrical system damage.

Challenges, Troubleshooting, and Solutions related while oil gets on the alternator

Challenges/IssuesTroubleshooting StepsSolutions
Oil Contamination Impact on InsulationRemove oil using an electric parts cleaner, focusing on contacts and windings. Check for and rectify any seal leaks to prevent recurrence.Inspect the alternator for visible oil presence. Check insulation resistance using a megohmmeter; a significant drop indicates contamination.
Increased Electrical Resistance & OverheatingDisassemble and clean the alternator, paying special attention to bearings and brushes. Replace brushes if below 5mm in length or if bearings show signs of contamination.Measure the alternator’s electrical resistance with a multimeter across the terminals. Compare temperature using an infrared thermometer to detect overheating.
Efficiency Reduction & Output DecreaseUse a multimeter to check alternator output voltage under load and idle conditions. Voltage below 13.5V indicates reduced efficiency.Clean the alternator internally and externally. Ensure all connections are free of oil and debris to improve electrical contact and efficiency.
Accelerated Wear on Bearings and BrushesListen for unusual noises and check for excessive play in alternator bearings. Inspect brush length and condition.Disassemble and clean alternator, paying special attention to bearings and brushes. Replace brushes if below 5mm in length or if bearings show signs of contamination.

This article will provide an in-depth examination of the effects of oil on alternators, clear solutions, and preventative maintenance to undertake.

What Areas of the Alternator are Impacted?

The two main components impacted when oil contaminates an alternator are the brushes and rotor. These internal elements are essential to the alternator’s function of generating electricity to power your vehicle’s electronics and charge the battery while operating.

What Happens if Oil Gets on Alternator

Image Credits: Replaced the 26yr old OE alternator belt (on a motorbike?) while the bimmer is apart awaiting replacement battery. BMW oilheads are very strange beasties indeed! By Ride Local Dream Global – Mike Mekinda  is licensed under (CC BY 2.0)

  • Brushes: Carbon traces that transmit current from stationary wires to the spinning rotor. Brushes are delicate and oil smearing causes rapid wear and contact failure.
  • Rotor: The rotating electronic magnet within the alternator. Oil on this component inhibits effective spin leading to low/no charge situations.
  • Bearings: This can also be affected depending on oil volume and viscosity. Contamination causes bearing seizure, eventually locking rotor spin.

Without urgent correction, your alternator will be rendered useless whenever oil penetrates these sensitive areas.

What Damage Happens with Oil Exposure?

Several types of deterioration will occur if oil seeps into an alternator over any period:

Brush Deterioration:

  • Oil impregnation leads to significant brush weakening
  • Carbon particles break under friction heat without dry lubrication
  • Contact tails corroded from oil residue increase resistance

Rotor Issues:

  • The buildup of Oil inhibits effective rotor spin essential for alternator charge
  • Added friction forces rotor seizure, overtaxes components
  • Magnet weakening

Bearing Problems:

  • Oil-degraded grease lubrication qualities
  • Particulate contamination gradually seizes the operation
  • Eventual lockup as oil residue solidifies

General Problems:

  • Short circuits from conductive oil bridging circuitry
  • Degraded wiring insulation allowing current leaks

These cumulative issues translate to wild voltage swings, unreliable charging, battery draining, and sudden alternator failure. Essentially the steady supply of electricity to your vehicle’s systems is compromised. Without correction, your battery will continue depleting until the vehicle shuts down or engine components reliant on electrical supply sustain damage.

How Does Oil Reach The Alternator Internally?

There are a few common ways oil can drip down into the alternator:

  • Excess engine oil accumulating on components above and dripping down
  • The rear main seal leaks allowing oil to coat the back side
  • Shared mounting points to the engine block transfer oil
  • Improper handling/filling during oil changes
  • Excess blow-by vapors condense and run out

While the alternator casing is sealed, aging gaskets/bolts allow oil ingress over years of engine movement and vibration. The contagion spreads internally the longer oil has access to the alternator’s working components. Moisture also enters the housing which when mixed with oil residue creates a thicker conductive gel multiplying issues.

Troubleshooting Oil Contaminated Alternators

Diagnosing oil-fouled alternators involves noticing these key symptoms:

Rotor Issues:

  • High-pitched whining from warning bearings
  • Lack of response from battery light when revving RPMs

Performance Problems:

  • Battery not charging/draining rapidly
  • Many Electrical faults (lights/components malfunctioning)

The main giveaway is a drop-off in alternator output identified via multimeter measurement. Most charging issues originate from oil contamination rather than component wear given an alternator’s lifespan.

Remove and inspect for signs of oil pooling in casing holes or dripping from rear assembly mounts. Check brushes/rotors for heavy dark staining. These visual queues coupled with the above symptoms confirm an oil-damaged alternator.

How To Fix an Oil-Soiled Alternator

  1. Remove the alternator from the vehicle
  2. Fully disassemble the component
  3. Clean using an electrical cleaner spray to dissolve the residue
  4. Check components for wear/damage
  5. Replace bearings and brushes
  6. Wipe down interior housing
  7. Reassemble ensuring proper alignments
  8. Test output efficiency on a bench supply
  9. Refit to vehicle if charging values normal
  10. Run engine and recheck charging system voltages

This alternator refurbishment allows rebuilding of the component to like-new output capabilities if caught early before permanent damage occurs.

Best Practice Prevention Tips

Blocking oil migration pathways down to the alternator keeps functionality intact for long time. Here are smart preemptive actions to take:

  • Use engine degreaser sprays and pressure washer concentrate on mounts/casings to deter oil transfer
  • Install aftermarket skid plate shielding under the alternator
  • Seal cracked engine covers dripping oil above
  • Replace leaking cam seals promptly
  • Fix worn turbo shafts blowing excess oil mist
  • Check alternator wiring gaskets and housing seals when inspecting belts/hoses

Routinely monitoring your charging system dashboard gauges also helps identify leakage-induced electrical issues before catastrophic alternator failure happens. At the first sign of over-under voltage warning lights, inspect for oil fouling and address.