Volkswagen is warning owners of VW Passats and Audi A4s about an engine sludge problem. The company won't say how many engines it has replaced or repaired so far.

Affected are turbocharged four-cylinder engines on 1998 through 2004 Passats and 1997 to 2004 A4s, Automotive News reported.

Consumers have been complaining about the problem for years. "At just under 36k miles my oil pump blew and the car went crazy," Tim of Grand Blanc, Michigan, said in a complaint to earlier this year.

"The oil pump was full of sludge (so they told me) which caused blockage and massive heat build-up, which blew out the turbo. $5000 later I received a call from the service manager who told me that it was ready to be picked up," Tim said. VW refused to pay for the repairs, he said.

It's the latest in a long line of quality problems for VW, which has seen its U.S. market share slip in recent years.

Sludge problems aren't unique to VW. The Center for Auto Safety is asking Chrysler to correct sludge problems and extend the warranty on 2.7-liter V-6 engines in its 1998-2002 model year vehicles. Many consumers have complained of problems in the engine used in the Dodge Durango

"My Dodge Durango oil gauge would show fine one second then terrible the next. If I let it cool it would be ok and then go back to 0 pressure when I got going," said Milet of Mart, Texas, in a complaint to "I showed them all the oil changes I had done and they told me I must have been getting ripped off because I had "sludge" everywhere.

Toyota has had sludge problems in its the 1MZ V-6 and the 5SFE inline 4 engines and faces the prospect of replacing or repairing 3.3 million engines.