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).
Oil level behavior in Wraith III & Bentley III engines, focusing on the risk of over-oiling.
| Identifier | ExFiles\Box 108\2\ scan0088 | |
| Date | 16th May 1938 | |
| Secret By.{R.W. Bailey - Chief Engineer} from Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell} c. Hs.{Lord Ernest Hives - Chair} c. RHC.{R. H. Coverley - Production Engineer} c. Da.{Bernard Day - Chassis Design} c. Da{Bernard Day - Chassis Design}/Jnr.{Charles L. Jenner} 600 400 Rm{William Robotham - Chief Engineer}/Swdl.{Len H. Swindell}1/R.16.5.38. WRAITH III & BENTLEY III OIL LEVEL. It has been very noticeable on the above units during development work that when starting up from cold with a normally full sump of 13-14 pts on the "maximum" mark, the oil level goes down to the zero stop in a very short time. In consequence it would be very easy to over-fill the sump which could result in several disadvantages, namely, leaking into the clutch pit and general over-oiling. The picture we have in mind is that of a car being started up cold and whilst warming up, the bonnet lifted and the oil level checked over, by which time the indicator would be reading zero, even though before starting the indicator could have been reading "maximum". In this condition it is feasible to assume that another gallon and a half might be added with the result that the sump would be over-filled by this amount. Upon investigation we find that the main quantity of oil is held up forward of the front compartment in the sump, and some time elapses before the indicator starts to return to normal due to the smallness of the balance hole in the sump web which does not permit sufficient flow to balance with the intake flow of the pump. These conditions are improved to such an extent that there is no danger of over-filling by any more than 3-4 pints by the following. The front sump web having a large oil balance hole equipped with a trap door, as per P.III, to prevent forward oil surge when braking. In this condition when the unit is started up with a full sump (13-14 pints) the indicator being on maximum, the pointer drops back only approx. 25% or down to a 10 pint oil level " in the sump after running. The reduction of 3-4 pints in the oil level is only the amount that is suspended in circulation as there is no building up in the front compartment. The reason why Wraith and Bentley III oil level drops back much more than 25/30 and Bentley II is due to the very large capacity oil pump and the freeness of the oil relief system. By the use of the large balance hole in the front web of the sump, the oil level drop is made much better than even the 25/30 & Bentley II. | ||