As of July 2007, there are still current news reports of used car buyers whose engines froze up just days after what they thought was a bargain. Sludge is gelled oil, thickened by overheating and contaminant build-up. Sludged oil galleries in the cylinder block or head deprive moving parts of critical lubrication.
Once the oil passages are clogged, the damage is done. Motor failure is just a matter of time. Subsequent proper oil change intervals will not stop the process. This is why a previous owner's service records are so important to used car buyers. Engine oil gelling is expensive, and can happen over and over in susceptible models.
Average reported mileage at engine failure is 63k miles, with some nearly new engines freezing up with as low as 15,000 miles. Most of these were under warranty, but claims were denied. A majority of the oil sludging occurred in former rental fleet cars, and lease returns, sold to naive bargain hunters.
Extended oil change intervals had been promoted for several years in the early 1990's. But strict emissions standards and fuel mileage standards changed engine design. Starting around 1996, problems with extended drain intervals developed.
There was an attempt to bury the story, then manufacturer denial took over. Almost every car manufacturer refused warranty claims, citing improper maintenance as the reason for sludged engines.
A few people just don't maintain their cars, but they don't all purchase these same failure prone models. If oil change neglect is the main cause, the sludging should be spread across every engine type and car model.
As the cover-up continued, internet automotive forums lit up with reports of claim denials, stonewalling, and poor customer service by automakers. Toyota, Saab, Audi, and Volkswagen ultimately stepped up, extending drivetrain warranties on sludging models. Chrysler refused to extend warranty protection or expedite the claim process. For vehicles engineered prone to sludge, there really is no solution.
For oil sludge prevention try the following. Change engine oil at least as often as the "severe service" or "severe climate" interval in the owner's manual. Replace the PCV valve, basically an oil vapor separator, every 30K miles. Retain every receipt for each service or repair, making sure the vehicle identification number (VIN) and description of service performed are clearly written. If your engine has overheated, replace the oil and repair the cooling system immediately.
Car buyers must learn to shop for more than the "best deal" and "low monthly payments." Many of these sludgers were "bargains." They were sold as new cars by fat incentives, easy credit lease contracts, and rental fleet volume deals. Car buyer beware.
