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 Vacuum Oil Company Limited discussing the viscosities of different Mobiloil Aero lubricating oils.
| Identifier | ExFiles\Box 145\1\ scan0056 | |
| Date | 30th November 1933 guessed | |
| Y56-12948 No. 2 V.O.Co., Ltd, to With regard to the question of the temperatures obtained in service with engine lubricating oils, we have made up a table which we are attaching hereto showing variations of absolute viscosities with temperature for Mobiloil Aero "W", Mobiloil Aero "H" and Mobiloil Aero "XH". You will see from this that Mobiloil Aero "W" approximates Air Ministry Specification D.T.D. 109 - in fact as regards viscosity it is within the limits imposed. Mobiloil Aero "H" and Mobiloil Aero "XH" are grades of similar quality but higher viscosity. In addition to the readings at 100°F and 200°F, we have included viscosities at 32°F as we feel these are of importance as indicating the relative ease of starting from cold with these three oils. In comparing the temperature at which these Mobiloil Aero Oils have similar viscosities, we find the following. The absolute viscosity of Mobiloil Aero "W" at 200°F is .190 centipoises, the corresponding temperatures for the other two grades being :- Mobiloil Aero "H" 220°F Mobiloil Aero "XH" 228°F Similarly at 32°F, we find that Mobiloil Aero "W" has a viscosity of 42.4 centipoises, the corresponding temperatures at which the other grades have this viscosity being :- Mobiloil Aero "H" 44°F Mobiloil Aero "XH" 48°F We feel that experience with Mobiloil Aero "H" and Mobiloil Aero "XH" is likely to be of considerable interest to you if oil sump temperatures much higher than 100°C are frequently experienced, because it should be clear from these figures that if, for example, a certain bearing in an engine gives satisfactory service with an oil of the class covered by Air Ministry Specification D.T.D.109 at 200°F, the important factor of oil viscosity can be maintained up to 228°F by employing Mobiloil Aero "XH", and we should expect that this would influence very largely the results obtained. Yours faithfully, VACUUM OIL COMPANY LIMITED Chief Engineer Automotive Department AD/LEB | ||