Oil sludge can be a major contributor to internal combustion engine problems, and can require the engine to be replaced, if the damage is severe. Sludge is usually caused by the presence of water in the oil, and can accumulate with use. Ways to minimize sludge production and accumulation includes performing frequent oil changes, performing mechanized engine flushing, or de-sludging, using synthetic oil, and following the manufacturer's engine maintenance routine. Toyota, VW, and Audi engines are known for oil sludge. Oil sludge that causes an engine to run poorly or even seize is a rare occurrence and typically happens only when oil changes have been neglected or if the car has been driven extensively with an extremely low oil level.
- Norris Schleeter and Melanie McCalmont (25 September 2005). "Oil Sludge: an expensive but preventable disaster". www.schleeter.com. Retrieved April 28, 2010.