After prolonged exposure to high heat, engine oil can oxidize and break down, forming deposits known as sludge. This gelatinous goo can block vital oil passages, resulting in thousands of dollars in damage or even requiring an engine replacement.
While sludge often results from poor upkeep, notably not changing the oil at prescribed intervals, some engines appear more prone to sludge buildup than others.
The Center for Auto Safety, a consumer advocacy group, has received over 3,000 complaints about sludge problems covering model years 1998 through 2005. A large majority concern the base 2.7-liter V6 used in the Dodge Intrepid before the 2003 model year. A relative handful came after that or concerned some engines used in the Audi A4 and VW Passat, Saab 9-3 and 9-5, and several Toyotas, again mostly before 2003. Engine failure due to sludge is a major problem for car owners, and automakers appear to have been slow to address it, generally linking it to poor maintenance rather than to a problem with the engine. Still, Chrysler has instituted an arbitration program that offers partial or full restitution to owners who can demonstrate that they changed the oil when they were supposed to.
In a related case, Toyota settled a class-action engine-sludge suit in 2007 that covered an estimated 2.5-million Toyota and Lexus vehicles made between 1997 and 2002. In that case, Toyota agreed to repair sludged engines for up to eight years from the time of purchase. While Toyota staunchly maintained that any such “oil-gel” problems are attributable to owners’ abuse or poor maintenance habits it did set up a mechanism to reimburse complainants. The language of the settlement appears to include reimbursement to those people who may have already paid to have their sludge damage repaired.
Sludge problems demonstrate the importance of sticking to the manufacturer’s oil-change intervals. Keep all receipts and make sure they include the date, mileage, and vehicle identification number. Consumers who own cars with sludge-prone engines should change the oil according to the “extreme use” schedule in the owner’s manual. Doing that and saving the records provides evidence that you did your best to protect the engine, should you ever have to make a claim against an automaker. Also consider using a synthetic motor oil. Synthetics have a higher tolerance for extreme heat.