▁convert ▁b iod ies el , ▁and ▁even ▁its ▁g ly cer ol ▁by product , ▁to ▁hydro gen . ▁ ▁Conc ern s ▁ ▁Engine ▁wear ▁Lub ric ity ▁of ▁fuel ▁plays ▁an ▁important ▁role ▁in ▁wear ▁that ▁occurs ▁in ▁an ▁engine . ▁A ▁dies el ▁engine ▁re lies ▁on ▁its ▁fuel ▁to ▁provide ▁lub ric ity ▁for ▁the ▁metal ▁components ▁that ▁are ▁constantly ▁in ▁contact ▁with ▁each ▁other . ▁B iod ies el ▁is ▁a ▁much ▁better ▁lub ric ant ▁compared ▁with ▁pet role um ▁dies el ▁due ▁to ▁the ▁presence ▁of ▁est ers . ▁Test s ▁have ▁shown ▁that ▁the ▁addition ▁of ▁a ▁small ▁amount ▁of ▁b iod ies el ▁to ▁dies el ▁can ▁significantly ▁increase ▁the ▁lub ric ity ▁of ▁the ▁fuel ▁in ▁short ▁term . ▁ ▁However , ▁over ▁a ▁longer ▁period ▁of ▁time ▁( 2 – 4 ▁years ), ▁studies ▁show ▁that ▁b iod ies el ▁los es ▁its ▁lub ric ity . ▁ ▁This ▁could ▁be ▁because ▁of ▁en hanced ▁cor ros ion ▁over ▁time ▁due ▁to ▁ox id ation ▁of ▁the ▁uns atur ated ▁mole cules ▁or ▁increased ▁water ▁content ▁in ▁b iod ies el ▁from ▁mo ist ure ▁absor ption . ▁ ▁F uel ▁vis cos ity ▁One ▁of ▁the ▁main ▁concerns ▁regarding ▁b iod ies el ▁is ▁its ▁vis cos ity . ▁The ▁vis cos ity ▁of ▁dies el ▁is ▁ 2 . 5 – 3 . 2 ▁c St ▁at ▁ 4 0   ° C ▁and ▁the ▁vis cos ity ▁of