Originally Posted by Big Wave Dave

I've been using Castrol 20w-50 in my 1980 240D manual with 273,000 miles for about 10 years. It was previously running on the same weight but Valvoline 15 years ago when my father passed. It has always been a warm weather Southern California car but I have no clue what weight he was using. No leaks and the engines clean but my question is should I switch to a synthetic since it's getting older? Or don't fix what is not broke....

1980 Mercedes 240D manual 273,000
2015 Ram 1500 EcoDiesel Turbo 30,000
2015 Jeep Cherokee EcoDiesel Turbo 20,000