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).
Observations and conclusions from tests comparing old and new ranges of engine oils based on dilution, cranking speeds and startability.
| Identifier | ExFiles\Box 145\3\ scan0255 | |
| Date | 18th February 1937 guessed | |
| - 2 - The following observations and conclusions have been drawn from the sequence of tests. (1) Dilution. The dilution of the sump oil was measured after the road run in each instance and it does appear that the new oils were less diluted than the old oils - with the possible exception of aero-shell. The road run was of course too brief to get really reliable results but it is considered that there is some indication that less dilution is occurring. Possibly the oil seal between piston and cylinder is better with these oils than with the old range of oils; this would retard the rate of dilution and hence reduce the total dilution since the evaporation of the sump diluent is a function of temperature and time. Old range Dilution. New range. Dilution Old Single 0.8% New Single 0.2% Old Double. 0.4% New Double 0.0% Old Triple. 0.8% New Triple 0.4% Old Aero. Trace. New Aero 1.2% (2) Cranking speeds, torques, currents. The new range of oils has considerably lower viscosities at -1°C than the corresponding oils of the old range. The result is a noticeable increase in cranking speed and decrease in torque and current. Cranking speeds at -1°C. Old range. Cranking speed. New range. Cranking speed. Old Single 155.5 r.p.m. New Single 175.5 r.p.m. Old Double. 111 " New Double 153 " Old Triple. 96.5 " New Triple. 121 " Old Aero. 97 " New Aero. 110.7 " Starter current at -1°C Old range. Starter current. New range Starter current. Old Single 154 amps. New Single 141 amps. Old Double 215 " New Double 162 " Old Triple 231 " New Triple 202 " Old Aero. 228 " New Aero. 213 " (3) Startability. After the cranking speed test and friction tests, the engine was started and the time noted before it could be said to be running. A curve has been plotted of time to start against √Viscosity and this seems to indicate that there is a linear relationship; in other words, this engine is unable to start before a definite amount of work has been done on the oil film and so increased the temperature until the engine friction torque is equivalent to the torque it is able to generate. The relation on this engine between time to start and oil viscosity appears to be Time to start = .406 √Viscosity - 12.6 where the time is in secs. and the viscosity in centipoises. The starting is therefore instantaneous when √V is less than 31.0, i.e. when V is less than 961 centipoises. | ||