How to Clean an Oil-Soaked Alternator

Best Methods to Remove Oil from Your Car’s Alternator Without Causing Damage

Cleaning an oil-soaked alternator is a task I’ve tackled a few times, and I can tell you firsthand that it requires the right approach to avoid causing damage to critical electrical and mechanical components. Over the years, I’ve seen too many people make costly mistakes by using the wrong cleaning agents, which can lead to alternator failure. If you’re looking to clean an oil-soaked alternator effectively, following the correct process and using the appropriate products is crucial.

Why Oil on Your Alternator Is a Problem

Heat Retention and Insulation Breakdown— Alternator windings, the internal fans, and the case vents are all designed to dissipate heat efficiently to prevent overheating. When oil and grease coat the windings, it acts as an insulator, trapping heat and preventing proper cooling. Oil and grease buildup on the vents block air movement and reduce cooling. Overheating is what causes early alternator failure.

Electrical Conductivity Issues— Most people think motor oil is non-conductive. That’s partially true; the base oil isn’t conductive. However, the anti-wear and anti-corrosion additives can be conductive under the right circumstances, and that’s what’s leaking into your alternator along with the base oil. Oil buildup can eventually cause short circuits and even reduced voltage output.

Corrosion— The accumulation of oil, grease, dust, and dirt can trap moisture and contaminants, leading to corrosion of the copper windings and other internal components. Corrosion inside the alternator can increase electrical resistance, which reduces current output and voltage. It can also cause the breakdown of rotor and stator windings.

Notice how the vents are blocked due to oil and grease buildup. That reduces cooling and shortens the life of your alternator.

Ok, But How Do You Clean An Oil Soaked Alternator?

Carefully! Seriously. Cleaning an oil-soaked alternator can make the problem worse. The official recommendation is to replace it. However, if you search the web, you’ll find lots of information on how to clean your alternator, and most of it is wrong and even dangerous.

I’ll walk you through a method that doesn’t use the harmful spray cleaners others recommend. But keep in mind that there’s risk in doing this. Your alternator may already be partially damaged due to degraded insulation. The cleaning process can remove the remaining insulation, causing the windings to short out and possibly start a fire. With that in mind, follow this advice at your own risk. You alone are responsible for weighing the risks of cleaning your oil-soaked alternator versus the officially recommended replacement advice.

Understanding What Alternator Components Need Protection

When you clean an oil-soaked alternator, you must consider the sensitive components inside. The rotor and stator windings, typically made of enameled copper wire, are insulated with polyimide films, epoxy resins, and mica-based insulation to withstand high temperatures and electrical stress. Using the wrong chemicals can degrade these insulations, leading to alternator failure.

Most Automotive Spray Cleaners Can Damage The Rotor And Stator Windings

Rotor and stator windings are typically made of enameled copper wire, using insulating materials like polyimide films (e.g., Kapton), epoxy resins, and mica-based insulation to withstand high temperatures and electrical stress.

Epoxy and polyimide insulation can be permanently damaged by strong solvents used in brake, carburetor, and electronics cleaners. Those cleaners often contain acetone, isopropyl alcohol, denatured alcohol, lacquer thinner, and Methyl Ethyl Ketone (MEK), all of which can degrade epoxy resins.  Alcohol, turpentine, mineral spirits, and citrus solvents can damage polyester and epoxy varnishes.

Oil usually soaks the stator windings and accumulates Greece and dust. Strong solvents can degrade and even dissolve the wire insulation, causing alternator failure.

Automotive Spray Cleaners Can Also Damage Bearing Seals

Alternators contain a sealed front and rear bearing; the seal material varies but is most commonly made from nitrile rubber, polyurethane, PTFE (Teflon), or Viton.
• Nitrile seals are vulnerable to Acetone, Benzene, Toluene, Xylene, methanol and ethanol, trichloroethylene, dichloromethane, and Acetone, causing swelling, softening, and the potential breakdown of the rubber structure
• Polyurethane Seals are vulnerable to acetone, toluene, benzene, xylene, methyl ethyl ketone (MEK), ethyl acetate, butyl acetate, methanol, ethanol, and isopropanol, trichloroethylene, dichloromethane by causing swelling, softening, discoloration, or complete breakdown.

Automotive Spray Cleaners Can Damage The Plastics Used In Alternators

Alternator manufacturers use a variety of plastics for the brush holder, electrical connectors, and solid-state electronics. Each of these plastics can be permanently damaged by using common automotive spray cleaners: Polyamide (PA, Nylon), Polyphenylene Sulfide (PPS), Polybutylene Terephthalate (PBT), Acrylonitrile Butadiene Styrene (ABS), Polycarbonate (PC), Epoxy Resins, Polyether Ether Ketone (PEEK), Phenolic Resins.

Avoid These Cleaners When Cleaning Your Oil Soaked Alternator

Brake Cleaner: There are two main types of brake cleaners: Chlorinated non-flammable and non-chlorinated highly-flammable. Both contain aggressive solvents that can strip the protective insulation from the rotor and stator windings.

• Flammable non-chlorinated brake cleaners often contain Acetone, Toluene, Xylene, Ethylbenzene, Methyl Alcohol, Petroleum distillates, Heptane, and Naptha.
• Non-flammable chlorinated brake cleaner usually contains Tetrachloroethylene (also known as perchloroethylene, a solvent used in dry cleaning establishments).

Carburetor Cleaner: Carburetor cleaner is too harsh for an alternator’s delicate electrical components. It contains Acetone, Toluene, Xylene, Methyl Ethyl Ketone (MEK), Naphtha (Petroleum Distillates), Butoxyethanol, Boric Acid Compounds, and Boric Acid Compounds. These chemicals can corrode the copper windings, degrade rubber bearing seals, and weaken the plastic housings. Additionally, carburetor cleaner tends to leave behind an oily film that can attract dirt and dust.

Electronics Cleaner: While safe for some electronic components, electronics cleaners lack the degreasing power needed to remove heavy oil buildup effectively. Some electronics cleaners also contain harsh chemicals like  Isopropyl Alcohol, Heptane, Hexane, Ethanol, Acetone, and Methyl Ethyl Ketone (MEK). However, they are usually in lower concentrations than brake or carburetor cleaners.

Recommended Cleaners To Clean An Oil Soaked Alternator

Instead of using harsh solvents, it’s best to opt for cleaners specifically designed for degreasing without damaging sensitive components. Some of the most effective options include:

Water-Based Degreasers: They effectively cut through oil and grime without harming the insulation, windings, or rubber components. Search for a water-based degreaser labeled as “safe for electrical components” or “non-corrosive.” They provide sufficient cleaning power without degrading the alternator’s protective coatings.

How To Use A Water-Based Cleaner to Clean An Oil Soaked Alternator

1) Disconnect the negative battery terminal and then all electrical connectors at the alternator
2) Remove the alternator from the vehicle
3) To contain the mess, Place the alternator in a stainless steel or plastic tray.
4) Lightly spray or brush the alternator with a diluted solution of water-based degreaser according to the directions on the label.
5) Let the degreaser sit for about 5-10 minutes to break down the top layer of grease and oil.
6) Dip a synthetic cleaning brush or toothbrush in the fresh cleaning solution and lightly brush the case, cooling fins, and exposed stator windings. Continue adding cleaner until the excess dripping starts to clear up.  WARNING: Avoid using wire brushes or abrasive tools that can scratch the surface and damage protective coatings.
7) Rinse with clean water to remove the cleaner and any remaining oil.
8) Tilt the alternator at various angles to allow water to flow freely through cooling vents and drain properly.
9) Proper drying is essential to prevent internal corrosion and electrical failures. Use low-pressure compressed air to blow out excess water from the casing, windings, and bearings.
10) Place the alternator in direct sunlight for several hours, or use a low-temperature heat source (such as a hairdryer) to aid in evaporation. If the weather isn’t conducive to sun drying, consider placing the alternator in a well-ventilated, dry area overnight.
11) Inspect it for any remaining oil residue or corrosion.
12) Check the bearings for smooth operation by spinning the pulley by hand.
13) Once you’re positive it’s dry, install into the vehicle and reconnect all electrical connection

WARNINGS:
Never submerge the alternator in water, as it can seep into the internal windings and cause irreversible damage.
Avoid overuse of any cleaner, even if it’s safe, to prevent excessive wear on the protective coatings.
Wear gloves and protective eyewear to avoid skin and eye irritation from degreasing agents.

©, 2025 Rick Muscoplat