You might be interested in the following. The year is 1950:
"Engine failures were still happening frequently. Strange as it might seem nowadays, the Hastings force at this time used re-cycled oil in its engines. An Oil-Cooler Flushing Unit was set up at Lyneham and the engine oil-coolers were fitted with back-pressure gauges. When the back-pressure reached a certain value, the cooler needed flushing. This was fine if the aircraft was at Lyneham but not quite so handy if it happened to be at Mauripur.
The oil-cooler shutters were also inefficient and "coring" was a common occurrence. This phenomenon was caused by the cooler getting too cold which allowed the oil in contact with the matrix to solidify. This drastically cut the flow of oil passing through the cooler, rather like a mechanical version of the narrowing of the human arteries. Consequently the temperature of the remaining oil flow escalated to dangerous levels. Coring was fairly common when the aircraft was forced to climb into cold air, such as was necessary to cross over the Massif in France, for example. Eventually, new oil-shutter seals were developed and this helped ease the problem enormously, but not before the Hastings had become known as the finest three-engined transport in the RAF!"
I find it quite mind-boggling that they even tried to use re-cycled oil.