Engine Oil

Oil forms a film between moving metal parts so they do not touch. It also carries heat away, holds dirt in suspension until the filter catches it, and protects against corrosion. Viscosity grades such as 5W-30 describe how it flows cold and hot. Beyond viscosity, manufacturers specify approvals (for example ACEA classes or their own standards). Diesels with particulate filters need low-ash oils. Variable valve timing and timing chain tensioners also depend on the right oil and pressure.

Grades such as 5W-30 describe viscosity: the number before the W relates to cold flow, the number after it to viscosity at operating temperature. Manufacturer approvals, for example from VW, Mercedes-Benz or BMW, specify further requirements.

The oil pump draws oil from the sump, pushes it through the filter and into galleries feeding bearings, camshafts, the turbo and tensioners, then it drains back. The oil pump draws oil from the sump through a strainer, the oil filter cleans it, and it is fed under pressure to bearings, the camshafts, the turbocharger and other parts before draining back.

Check the level regularly and change oil and filter on schedule. Low level or the wrong oil can cause timing chain noise, variable timing codes, turbo damage and, at worst, bearing failure. Check the dipstick or on-board oil level display regularly. Running on too little oil, or on oil that is long overdue for a change, can damage bearings, chains and turbochargers quickly.