This 14 year old article may provide some insight: The Best Oil for Older Cars from Patrick Bedard’s commentary in Car & Driver November, 1999, p.23 The technical information in the column came from one Ed Kollin, who was a research chemist at Exxon for many years and who now is Director of R&D for Lubrication Science in Jersey—in other words, a guy who almost certainly knows what he is talking about. Here are some of the relevant facts: 1. Remember the synthetic oil ad that showed an engine running after it had first been filled and then drained of oil? Apparently the oil contains a 'miracle molecule' that allows the engine to run for a while after the oil has been drained. The 'miracle molecule' does this by clinging to the metal surfaces very tightly, so tightly that it displaces the anti-wear additives in the oil which were put there to protect those metal surfaces. This means that for long-term use, that oil actually wears your engine faster than conventional oil. 2. Today's motor oil meets SF specs. (now SL) --- the oil our older car engines were designed to meet something like SA or SB, or at most SC specs. (This is the SAE specification on the little circular label on every good motor oil sold in the USA). Usually we are told that the newer oil is better, but is it true? And if true, better in what way? 3. Engine oil contains many additives, and the primary anti-wear and anti-oxidation agent is a chemical by the jaw-breaking name of zinc dialkyi Dithiophosphate (ZDDP for short). ZDDP, while good for engine wear and reducing corrosion/rusting, it is bad for catalytic converters: as a result the modern SJ and later rated oils have about 25% less ZDDP than the old SA and SB oils. 4. New cars, to make the catalytic converters live, need lower levels of ZDDP. But this is a compromise, which results in more engine wear and corrosion. Our older precatalytic cars want a big dose of ZDDP to keep engine wear down. 5. New engine oil may be good for catalytic converters, but are not as good for your engine from the point of reducing corrosion as the old oil was. 6. Fuels today often have oxygenates - MTBE or Ethanol added to them in big cities in the USA. Traces of these oxygenates get into the engine oil, and apparently these chemicals are, to quote "tremendously corrosive", and they attack gaskets, seals and certain metals. No problem for automakers, they choose new polymers and alloys which are immune to these attacks. But what's to prevent the attacks and corrosion in older engines? 7. So what can we do? Well Ed Kollin says that for a seldom driven older car, such as show cars or in fact anything but a daily driver, "corrosion is a greater problem than wear, even the wear from starting an engine that has been sitting long enough to drain oil off most of its rubbing surfaces-- because only one little patch on that same rubbing surface is dooms day". 8. Ed goes on to say that while he can design a custom oil for this problem, the best off the shelf oil is heavy oil designed for Diesel trucks. Instead of SJ, look for combinations that begin with C (for compression ignition), CC-4 is the latest, preceded by CF-4, CF-2 and CF.A. Few oil blends meet both C and S requirements. While the oil part of these Diesel oils has the same lubricating qualities as passenger car oil, the most common heavy-duty viscosity is 15W040; more syrupy. But the Diesels get bigger doses of the additives---up to 50% more ZDDP (the anti-wear anti-corrosion additive) and 30 to 50% more detergent, dispersant and corrosion inhibitors. 9. The bad news: There's a very small chance, he says, that nitrogen compounds in the high dose of dispersant may cause some seals to leak. Moreover, if you've never used detergent oil before, you may wash chunks of sludge loose that could block the hydraulic filter. 10. The good news: If you have sticky rings, erratic compression and blue exhaust smoke, this high detergent oil will quickly free them up. For corrosion, Ed says, heavy-duty oil is the silver bullet solution. It's blended to neutralize the sulphuric acid produced by the high sulphur Diesel fuel. Note that sulphuric acid is also produced in car engines burning gasoline. However, the Diesel fuels contain more sulphur and consequently create more acid when burned. That’s basically all the really important information in the column. To me it contains at least three surprises--- (i) Some synthetic oils wear your engine out faster than conventional oils. (ii) Older conventional oils protect your engine better than the newer ones. (iii) The best oil to use in the older cars is an oil designed for Diesel trucks Posted by johnlayzell 14/12/2013 15:16:58
