If there's water present beneath the oil, such as a very large storage tank or the tank of a large dry sump, it's been known for microbes to grow on the oil-water interface. This is much the same thing as the bugs that can contaminate diesel fuel. These critters are acidic and cause serious damage. I'm not aware of a biocide that can be used in oil sumps and preserve the lubricating ability of the oil. A biocide does work well in fuel. The only cure I've heard of is to clean the oil system with steam that'll kill the bugs with heat, although there may be biocides that work and I've not heard about them. The main preventive is to keep water from accumulating in the bottom, either with centrifuging or coalescing filters.
Ken
[ August 17, 2003, 05:19 PM: Message edited by: Ken2 ]