When Oil Gets Old
Oct. 4, 2019—An article at MSN Autos takes a look at the mechanical and chemical effects that old engine oil can have on a vehicle.
Impurities, carbon buildups and blow-by are all covered, and they're exacerbated by old, dirty oil.
"As wearing accumulates, more blow-by occurs, which accelerates the wear and allows more blow-by. A nasty cycle, indeed. Dirty oil also contributes to wear on bearing surfaces, which reduces oil pressure," author Craig Gustafson said in the article.
He adds that oil gets contaminated at the molecular level as well, and its low-viscosity properties get less effective over time.
Gustafson adds another interesting note about one reason longer drain intervals are possible: less lead. He said that lead used to be a common "anti-knock compound" in engine oils. Lead was also a major oil contaminator, so longevity has improved as the use of lead waned. He also notes that oil formulation, engine design and wider use of synthetic oils are also major contributors.