🔍 Key Concepts

• How oxidation affects diesel engine lube oil over time • Common contaminants and deposits found in used lube oil • Differences between pitting, sludge, and varnish in engine parts

💭 Think About

• Think about what happens to lube oil when it is exposed to high temperature and air for long periods • Consider which types of engine damage or deposits are commonly linked to degraded or oxidized oil • Ask yourself whether oxidation typically leads to just one kind of problem, or if it can create multiple types of damage and deposits

✅ Before You Answer

• Be clear on what pitting is (surface damage to metal) versus sludge (soft deposits) versus hard varnish (hard, sticky film) • Recall what maintenance manuals say about oxidation by-products in lube oil and the kinds of deposits they form • Verify whether oxidation by-products are usually limited to one effect or can contribute to several different problems in the lubrication system