Forum:
I am currently using Shell Rimula R3X 15W-40 for my F73 (DL42 N/A engine). Now I am somewhat interested in using Mobil Delvac MX 15W-40 only because the classification is higher (CI-4). Whether the protection given to my engine would be better? Or actually Shell's good enough for my engine? Thanks for your opinion.
Rimula is the better option
Rimula is the better option for your engine if it is readily available. Remember these engines are old engines, as such the oil specifications are also very old.
Use only mineral or semi-synthetic oils, never use full synthetic oils in these engines. Full synthetics have an oil film which is far too thin as these engines have huge clearances when compared to new engines.
Continue to use Rimula
Thanks for the opinions, then for the next oil change I'll keep using Rimula R3X.