Chemical Wear/Degradation

Definition and Key Role

Chemical wear refers to the degradation of material properties, surface deterioration, or loss of substance in automotive components caused by chemical or electrochemical reactions under specific operating environments or exposure to chemical media (such as fuel, engine oil, coolant, and ambient air). Unlike mechanical wear, chemical wear is typically subtle and insidious, altering material structures at the molecular level. It is the primary cause of failure in modern long-life vehicle components, including sensors, sealing systems, and anti-corrosion coatings.

Common Forms of Chemical Wear

Oxidation & Corrosion: 

Acid Corrosion: Combustion by-products (such as sulphur dioxide and nitrogen oxides) blow by into the engine oil and react with moisture to form acidic compounds. These corrode critical metal surfaces inside the engine, such as crankshaft bearings and piston rings. 

Electrochemical Corrosion: In the cooling system, if the coolant's pH level becomes unbalanced or degraded, it creates an electrical potential difference that corrodes the aluminium radiator core or metal piping, eventually causing pinhole leaks.

Material Hardening & Embrittlement (Degradation & Embrittlement):

Rubber Ageing: Exposed to ozone, engine oil, fuel, or intense heat, rubber seals and hoses undergo oxidative cross-linking. As they lose elasticity and turn brittle or cracked, sealing integrity fails, resulting in oil or vacuum/air leaks. 

Surface Deposition & Gumming (Deposition & Gumming):

Carbon & Gum Deposits: Under high operating temperatures, fuel undergoes polymerisation, forming sticky gum deposits on fuel injectors and intake valves that hinder fuel atomisation and air intake efficiency.

Electrochemical Degradation:

Battery Degradation: During charge-discharge cycles in electric vehicle (EV) traction batteries, parasitical chemical side reactions occur within the electrolyte. This thickens the solid electrolyte interphase (SEI) layer and triggers structural lattice collapse in the electrode material, representing the core chemical mechanism behind battery capacity loss.

Diagnosis and Assessment Criteria

Diagnosing chemical wear is characterised by significant latency and distinct physicochemical indicators:

Oil/Fluid Analysis: The most definitive diagnostic tool for chemical wear. It tests the engine oil's Total Base Number (TBN, reflecting its acid-neutralising reserve), Total Acid Number (TAN), and moisture/contaminant levels. A depleted TBN paired with a rising TAN signals that chemical wear has entered a critical stage. 

Surface Colour and Texture Inspection: Borescope examinations that reveal abnormal reddish-brown rust, white powdery corrosion spots, or hardened surface micro-cracking point to clear evidence of chemical wear.

Electrical Parameter Measurement: On electronic sensors, chemical contamination (such as silicone poisoning) leads to signal output voltage drift. Technicians can trace chemical degradation on the sensor surface by referencing standard operating voltage windows.

Why is Chemical Wear Often Overlooked?

Long Latency Period: Unlike mechanical wear, chemical wear produces no immediate knocking, clattering, or abnormal noises. It silently alters material properties, meaning that by the time physical symptoms surface, the component is often already critically compromised.

Maintenance Misconceptions: Vehicle owners frequently focus solely on engine oil viscosity while neglecting the depletion of antioxidant additives; similarly, they listen out for unusual engine noises while overlooking the hidden risks of coolant-induced corrosion. 

Prevention and Countermeasures 

Strictly Adhere to Service Intervals: Over time, essential additives such as antioxidants and corrosion inhibitors in engine oil, coolant, and brake fluid become completely exhausted. Regular replacement is vital to break the chain of chemical wear. 

Control Fuel Quality: Avoid using low-grade fuel with high sulphur content, as high-sulphur fuel serves as the primary catalyst for acidic corrosion inside the engine. 

Maintain System Integrity: Ensure all lubrication and cooling circuits remain properly sealed to prevent external moisture and air ingress, thereby cutting off key chemical reaction media. 

Technological Development Trends

Chemically Resilient Materials: Engineering advanced polymer seals (such as fluoroelastomers/FKM) capable of resisting harsh and complex chemical media over extended service intervals.

Self-Healing Coating Technologies: Applying specialised nanocoatings to critical metal surfaces that automatically trigger a passivation reaction when corrosive agents strike, preventing chemical wear from penetrating deeper into the substrate.