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).
Summary of findings on oil cooling, oil consumption, and the performance of different sump designs.
| Identifier | ExFiles\Box 179b\3\ img313 | |
| Date | 13th March 1933 | |
| -4- SUMMARY. (1) We do not know any practical means of reducing the heat to the oil. (2) Reduced oil pressure will not make oil cooling any easier, but may be desirable as a means of decreasing oil consumption. (3) Promoting turbulence in the sump by directing the relief valve oil onto its surface by jets increases the efficiency of the bottom half as a cooler by about 15% at 100°C. (4) Even with turbulence we have about 200 B.Th.U's excess heat with the plain bottom half, and 170 with the ribbed bottom half, which at present will have to be dealt with by a separate cooler to ensure safe bearing temperatures with whitemetal. No.956 indicates the existing situation on the road. (5) To deal with the higher figure, a water or air oil cooler of approx. 80 cu.ins. capacity would be required. A high oil velocity is desirable through such a cooler. (6) We have had no experience with Kelmit at high oil temperatures, but since it has a considerably higher melting point than whitemetal, we anticipate that 120°C would not harm it. We are making tests to see. From inspection of the last 10,000 miles car, apart from the oeariage, the engine does not particularly mind high oil temperatures. These undoubtedly affect consumption, however, since they increase the flow through the bearings. (7) If the ribbed sump was finned internally to the same extent as it is at present externally there appears to be a probability that the excess heat units/min. un-cooled might be reduced to below 100. At the moment we are not getting full value out of the existing ribs. On the other hand the last 10,000 miles run shewed that the external ribs towards the rear of the crankcase tend to become choked with mud. Therefore, on the whole, cooling the oil utilising the bottom half is not easy or satisfactory. (8) For complete satisfaction we believe 100°C with 50 lbs/sq.in. oil pressure, or 85°C with 20 lbs/sq.in | ||