Giving the Nudge to Engine Sludge
Question: My 1985 Cadillac has sludge in the motor at 83,000 miles. I bought this car from a leasing agency, and I think the oil was not changed regularly. I have maintained the car and have had no problems. To remove the sludge, I have been advised to put a quart of transmission fluid into the engine and run it for 10 miles. What do you think?--H.
Answer: It sounds like another wild scheme dreamed up by a back-yard mechanic. These homespun car remedies often have some merit, but not this time. The transmission fluid won’t damage your engine, but neither will it help.
Engine sludge is the accumulated dirty oil, tars and carbons that build up in the crankcase or in the upper valve areas. It is caused by either improper maintenance or a poorly designed engine.
When an engine does not receive regular oil changes, dirty oxidized oil combines with emissions and forms a gooey tar that attaches to the engine crankcase and valve covers. At its worst, the sludge can impede lubricating oil, wear down parts and possibly cause overheating in areas where the engine block is insulated by the sludge.
An engine’s crankcase and valve areas are supposed to be properly ventilated to carry off fumes that blow through seals from the combustion chamber. These gases are supposed to be drawn out by what is called the positive crankcase ventilation system and recirculated through the combustion chamber to be burned off.
Auto makers have worked to make engines cleaner burning. This theoretically means that new engines should have less sludge. But some ventilation systems are poorly designed, according to Norm Hudecki, an oil expert at Valvoline.
Ford had a particular problem with some of its huge 5-liter engines for its big cars, including the Lincoln Town Car, providing at least part of the motivation for the oil industry to develop better oils.
Sludge can build up inches thick inside a big, poorly ventilated engine that has not received regular oil changes. The sludge is often like tar, but sometimes it is like a caked dirt.
Once you have a sludge problem, there is no way to make the engine clean again short of disassembling the engine and scraping it clean.
Many auto supply stores sell engine flushes that claim the ability to wash out engine sludge and dirt. But using a flush, which is basically just kerosene, is risky business.
Sometimes, these flushes can dissolve some of the dirty sludge. But if a piece of sludge is just dislodged rather than dissolved, it can easily plug up small oil passages and cause serious engine damage.
A better solution might be to simply do several oil changes. It is likely that the first time you changed your oil, the new oil looked dirty almost immediately. If you repeat the oil change several times, you can safely rid the engine of superficial sludge.
The remaining sludge may not do any engine damage, but it may tend to degrade new oil more quickly. So, you may want to perform more frequent oil changes for as long as you own the car.
