DB1, the moderator stated very clearly why that specific thread was closed. I believe it was a proper move.
I also believe it was done to keep sludge discussions open and informative, and not have them become yet another political platform for those who seem to want Toyota's head on a plate for self serving reasons.
Cherry128's response puts the issue into perspective quite candidly. I need not go into detail in that regard. It just isn't that big a problem, as some would have us believe.
Sludge has been around since internal combustion engines were invented. There may very well be occurences due to the statistical probability that some engines have a bad component no matter how stringent the Quality ****urence program may be--that's an inevitability of the mass production process common to all manufacturers, and I won't exclude that as one reason for sludge.
But the most common cause by far and away is failure to change oil when it's time to do so. That's my take on the issue, and after 38 years in the engine repair/rebuild business, I can attest to it being true. I also wish to point out that my shop is an independent business, and not affiliated with Toyota in any way.
A recent article in Automotive News is very enlightening, and is probably the closest we're ever going to get as to what the root causes are in the sludge issue. I have copied the following excerpts:
"Bob Orlee, a GM engine engineer who specializes in oil issues, said GM has installed oil life monitors because many consumers did not read their owner manuals to learn when they should change their oil.
He also said some consumers didn't know that severe driving areas, such as those with high heat and heavy traffic, required them to change their oil more frequently.
He said synthetic oil likely won't prevent sludge buildup.
Confusion abounded
"We realized in research back then when we talked to customers that they had no idea if they were severe or moderate drivers," he said. "Even with all those words we put in owners' manuals it was so difficult to describe to people when they should do an oil change. The oil life monitor simplified the maintenance procedure."
GM began using oil life monitors in the 1980s.
Chrysler engineers say improper maintenance is the likely reason for sludge buildup in some vehicles. About 70 percent of the vehicles with sludge-filled engines were sold to rental car fleets before consumers bought them as used vehicles, Locricchio said.
"The second or third owner can change oil on time, but if the first owner didn't, the engine can be susceptible to sludge," he said.
VW recommends oil changes at 5,000 miles or six months, or more frequently when climate or driving conditions are extreme.
Chrysler says owners should change oil every 3,000 miles in city driving or every 7,500 miles in highway driving.
Toyota Motor Sales U.S.A. Inc., which wrestled with a sludge problem in 2002 and 2003, denied there were design flaws in some of its four- and six-cylinder engines and also pointed to consumers for the problem. But Toyota extended warranties, replacing engines for free and changing the oil breather system in valve covers.
Orlee, the GM engineer, said sludge always has been a problem for engines. But improvements to motor oil and engines have reduced problems.
Said Orlee: "Sludge has to do a lot with how you drive. classic sludge was related to low-speed operations, like in taxicabs. Some of the sludge out there now we believe may be a different form of sludge. Some of it happens only in hot climates."
Please note the second last paragraph. I fully believe this is the answer to all the questions and theories surrounding the issue.
