Sludge: jumping through hoops to make a case.(Automobile industry working to provide sludge protective engines)

A killer named sludge may live in your engine and can choke the life from your car, regardless of maintenance or mileage And the automakers whose engines are susceptible to sludge still aren't always eager to help.

Sludge often forms when oil oxidizes and breaks down after prolonged exposure to high temperatures. The baked oil turns gelatinous and car block vital oil passages, which could lead to repairs exceeding $8,000 or even an engine replacement.

While sludge often result from poor upkeep, notably not changing oil at prescribed intervals, some engines from Audi, Chrysler, Saab, Toyota and Volkswagen appear prone to it (see the chart below).

The Center for Auto Safety says it has received about 1,300 sludge complaints since 2004. Toyota, the company with the most engines in question, cited 3,400 complaints through 2002 but hasn't provided an updated number since. And while about 4.7 million engines sold in the U.S. may have sludge-prone designs, the problem rate as reflected in our reliability data is very low But that's little solace to those affected by it.

The automakers initially blamed these concerns on poor care and resisted covering repair costs. However, all but Chrysler have begun replacement or repair programs, even for those who bought heir vehicles used. Chrysler says it will handle sludge complaints individually.

AUTOMAKERS PLAY TOUGH

These programs put the burden of proof on the owner, y however. While Toyota, Lexus, Audi, Saab, and Volkswagen have extended engine coverage to eight years from the original purchase, the deals come with fine print.