From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Letter from a customer inquiring about the correct engine lubricant viscosity for their Bentley car.
| Identifier | ExFiles\Box 88\1\ scan0210 | |
| Date | 15th November 1935 | |
| E.{Mr Elliott - Chief Engineer} P. SWENSON S. M.{Mr Moon / Mr Moore} SWENSON S. R.{Sir Henry Royce} SWENSON S.M. Swenson & Sons 52 Wall Street New York November 15, 1935. Bentley Motors (1931) Ltd., Derby, England. B-78-EF Dear Sirs: I wish to thank you for your various letters concerning my Bentley car, all of which I would have acknowledged more promptly except for my absence from the city. I do not wish to be unduly inquiring, but on the other hand I am anxious to be sure that I use the proper lubricants. In your letter of September 25 you recommend Vacuum Mobiloil BB for normal temperatures, and Grade A for zero temperatures. However, in the instruction book you recommend for normal temperatures Mobiloil D, which apparently closely corresponds in viscosity to the BB grade sold in this country; and for zero temperatures you recommend Mobiloil AF. Grade AF, I believe, as sold in your country, is the same as Grade AF sold in this country by the Vacuum people, and in viscosity is intermediate between BB and A.{Mr Adams} In other words, using the designations applied to their oils in this country, the different viscosities sold by the Vacuum people are as follows: B -- equivalent to S.A.E. viscosity rating 60 BB -- " " " " " 50 ✓ AF -- " " " " " 40 ✓ A -- " " " " " 30 Arctic -- " " " " " 20 As you probably know, it has become the practice in this country to designate different viscosities by the S.A.E. numbers which are used by all the oil companies. In other words, the oil which you recommend for normal temperatures is S.A.E. 50, and for zero temperatures S.A.E. 30; and inasmuch as the instruction book calls for AF, which has a viscosity of S.A.E. 40, I would appreciate it if you would advise me which is correct - the information given in your letter or in the instruction book. I believe it is not usual to specify so great a variation in viscosity between oil for normal temperatures and for zero temperatures as there is between Mobiloil BB and Mobiloil A.{Mr Adams} | ||