After prolonged exposure to high heat, engine oil can oxidize and decompose, forming deposits called sludge. This gelatinous paste can block vital oil passages, resulting in thousands of dollars in damage or even requiring an engine replacement.
While sludge is often the result of poor maintenance, including not changing the oil at prescribed intervals, some engines seem more prone to sludge build-up than others. (See the table below.)
The Center for Auto Safety, a consumer advocacy group, has received over 3,000 complaints about sludge issues spanning the 1998 through 2005 model years. The vast majority are for the base 2.7-liter V6 used in the Dodge. Intrepid prior to the 2003 model year. A relative handful came after this or involved certain engines used in the Audi A4 and VW Passat, Saab 9-3 and 9-5, and several Toyotas, again primarily prior to 2003. The Outage Muddy engine failure is a major problem for car owners, and automakers seem to have been slow to address it, generally linking it to poor maintenance rather than an engine problem. Still, Chrysler has implemented an arbitration program that offers partial or full restitution to owners who can show they changed the oil when they were supposed to.
In a related case, Toyota settled an engine sludge class action lawsuit in 2007 that covered approximately 2.5 million Toyota and Lexus vehicles manufactured between 1997 and 2002. In that case, Toyota agreed to repair fouled engines for a period of time. period of up to eight years from the time of purchase. While Toyota has firmly argued that such “oil freeze” problems are attributable to owner abuse or poor maintenance habits, it has put in place a mechanism to reimburse plaintiffs. The wording of the regulation appears to include reimbursement to people who may have already paid to have the sludge damage repaired.