Thanks everyone for the replies to my question about 5W-30 oil. Now I understand.
A couple of you sent replies like this one from Paul: "At one time powerplant experts thought that wider bearing clearances and heavier oil offered optimum protection. Eventually they discovered that lighter oils and tighter clearances resulted in less wear, better power and better fuel economy. What's more the 10W-40 oils sometimes caused sticking of rings under some conditions. Not good." Does anyone know when this change in engine design took place? My 1989 Volvo 740 has 230,000 mi./370,000 km. and burns no oil. I have been using Castrol synthetic 10W-40 oil in it year round. Should I switch to 5W-30 or continue with the heavier oil? My wife was advised to use 20W-50 in her 1967 Austin-Healey Sprite. Should she change to something lighter? Thanks again, Joe -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
