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Mobil 1 (and I presume most synthetics) have a Diesel-use API service rating shared by Chevron Delo and other lube oils intended for turbo diesel engines. The significance of this is superior anti-wear and anti-corrosion properties, according to a Car & Driver column by Patrick Bedard a few years ago. A consultant in lube oil additive package design was Bedard's source. The focus of that article was lube oils for old cars that are not in daily use, and which collect moisture and acids, and get started with dried-out wear surfaces.
It was claimed that lube oils marketed for catalyst-equipped cars are being given less of those addditives, to cater to catalyst health, and that we should avoid oils that are not rated for diesel engine use, ie, that have only two-letter API designations beginning with "S." Diesel-use designations begin with "C", such as CH.
Considering the known cam and lifter wear problems in B18 and B20 engines, it seems advisable to use lube oil with the best wear and corrosion resistance, and in a thin enough viscosity that it readily wets those parts by splash and mist.
Synthetics that I have used all seem to seep past gaskets and seals more readily than natural oils. I use Mobil 1 now in a DOHC catalyst car 14 years old (mixing 10-30 with 20-50) and Delo 15-40 in a 38-year-old, un-overhauled, pushrod-engined car that has cam and lifter wear discovered 25 years ago during a valve job.
C.O.Greenlaw, Sacramento Cal.
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