Glycol Contamination

Canonical Definition

The presence of ethylene glycol (engine coolant) in engine oil or gearbox fluid, resulting from failure of an engine oil cooler, cracked cylinder head, failed head gasket, or cracked engine block. Glycol combines with engine oil to form a thick gel sludge that dramatically increases viscosity, creates abrasive deposits on bearing surfaces, and degrades oil film strength. As little as 0.1–0.5% glycol by volume in engine oil causes bearing damage; concentrations above 1% can lead to complete bearing failure and engine seizure if not detected and corrected immediately. Glycol presence is detected by FTIR spectroscopy or by the potassium test (elevated K indicates glycol inhibitor package entry).

Engineering Context

Glycol contamination is a maintenance-ending event if not detected early. Periodic oil analysis detects glycol intrusion 50–200 operating hours before visible symptoms appear — white exhaust smoke, milky oil under the filler cap, coolant level loss, or overheating. Upon confirmed glycol contamination, the oil and filter must be changed immediately, the contamination pathway identified and repaired, and the lubrication system flushed with clean oil before returning to service. Running equipment on glycol-contaminated oil even briefly multiplies the damage compared to a timely shutdown.

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