Stan,
I was always told You know you musn't believe everything you are told. Apparently, still one in five of UK school children still believe the Sun goes around the Earth
At least at the school I am at, a lot more students know the sun never actually stops shining and that it
appears to rise in the east and
appears to set in the west. Some of them even know how fast they are moving whilst standing still.
Back to the oil. The CS was never fitted with a filtration system because it was designed 70 years ago and used previous engine technology as a basis for the design.
Very few stationary engines, in those days, had a filtration system and if they did it was most likely a bypass system. The rest relied on sedimentation and recommended regular sump (oil pan) removal and cleaning. Sludge was a big problem in gasoline and kerosene engines and more so when they were suddenly changed to the newer 'detergent' oils of the 50s. Many suffered blocked oilways and major failures because of that change, without being prepared for the extra sludge being cleaned from the engine.
Modern oils are streets ahead of those lubricants. Most new engines have full flow filters and some employ a bypass filter as an additional safeguard. Now that very low sulphur fuels are available I would expect two things - either the oil can be made to last longer or the oil companies will reduce the additive packs (while still increasing the prices
). I suspect the latter.
In any case, these days the detergent oils will carry the collidal particles in suspension and they have been demonstrated as making no problems regarding engine wear. The larger particles will either be filtered by a full flow filter before there is any possibility of that particle circulating to a bearing, or, as in the case of the CS, settle by gravity in the sump.
The main barrier to sedimentation in the CS is probably the oil viscosity. They were long lived despite relying on that system. Lets face it most engines were stood overnight and that was probably long enough to encourage the larger wear-causing particles to settle below the pump outlet screen, followed by gently collecting on the bottom of the sump. The oil pump system on the CS was/is of such simple design that it is never stressed, rarely ever fails (because of it's simplicity and not requiring any extra components like pressure relief valves, full flow filters, etc). All pumped oil in a pressure fed system is forced into and through a bearing, unless it is returned to the sump via the pressure relief valve. The CS only uses the amount of oil it needs - very much less than that passing from a pressure system.
Anyway, bottom line is that it has nothing to do with a detergent oil or non detergent oil or nothing to do with whether it has a filter or not. Just a different design system. The Lister was a KISS system. All my 1930/40s tractor engines used non detergent oils and had bypass filters. They now work perfectly well on detergent oils and a bypass filter. In fact better now than with those early poorer lubricants.
Regards, RAB