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...to experience leakage after switching to synthetic, as it does happen-- but I think it depends on the relative condition of the seals and gaskets in the engine more than anything. I'm not saying that your problem was imaginary and unrelated to the oil transition, but that in most cases of these mid-life alterations reported here on TSN and others I'm aware of, no problems have been encountered. I think leak problems of this nature are the exception rather than the rule.
My understanding is that in addition to R&T's observations (quoted earlier), as fossil oil oxidizes and creates sludge and varnish, the accumulated crud can actually mask the presence of bad seals and gaskets by acting as a seal itself. As the synthetic oil begins cleaning the crud out and not adding to it, that secondary sealant disappears and reveals the failing gaskets by leaking. My opinion is that if sludge is masking a bad seal or gasket, it's time to change it anyway.
Again, I've never had a problem and most don't, but I agree that the older the engine the more chance of experiencing a leak, and although I think the 50k-mile recommendation might be reasonably accurate, it really depends on how well maintained the car has been up to that time. If the engine was subjected to frequent starts and stops, long oil-change intervals, and a general lack of maintenance, the potential for trouble would be worse than a car that was more meticulously maintained. My experience deals with cars with <35k miles on them when the transition was made, which may be a factor in my success and that of others.
Be that as it may, I think Dick, the Amsoil salesman, has good ideas along these lines: On older engines, run a flushing oil (like Amsoil or BG) through the system first, then change oil quickly (3k) for the first two or three changes. I didn't flush my '95 Aero when I received it at 35k, but it did take two or three changes before the remnants of the old fossil oil were eliminated, judging from lab tests. Fortunately, I didn't have any bad seals or gaskets, so I had no leakage.
posted by 68.11.185...
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