Examining engine sludge

By Tom Torbjornsen

Dear Tom,
I own a 2000 Lexus ES 300 Platinum Series. I purchased it 3-1/2 years ago, and at the time it had only 4,400 miles on it. It now has nearly 39,000 miles. It seems to be running fine and the Lexus dealership has never indicated any problems when I get the car serviced. However, I wonder whether there might be sludge buildup because the car sat idle in its early years. Could this be a problem later on? And would it be evident by now?
Michael from Long Island

I doubt your car has sludge buildup as a result of the car sitting. What causes sludge? When oil wears out it loses its ability to lubricate. As a result, excessive heat from friction causes oxidation, and the combination of oxidation and excessive heat causes sludge. Keep the oil changed according to manufacturer’s severe service specs and you shouldn’t have a problem.

What is sludge and how does it form?
Sludge is a nasty, gross, hardened buildup of oxidized oil that forms as a result of not changing your oil (according to manufacturer specs). Old oil that doesn’t lubricate well causes an increase in friction between engine parts and thus the engine temps increase. When sludge sets up inside the engine, it builds on itself and inhibits the flow of oil, causing even more problems with internal lubrication. The result? Premature wear and, ultimately, premature engine failure. Contrary to Michael’s concern, sludge does not set up as a result of an engine that is rarely used. It occurs due to extensive engine use in an environment where the engine is not maintained (infrequent or no oil changes).

How do I stop sludge buildup in my engine?
You can control sludge buildup by maintaining a vigorous maintenance schedule according to the severe service schedule in your owner’s manual.

Years ago sludge was a common occurrence caused by inferior engine oils that lacked the detergency aspects of today’s oils. Back in 1974 a customer of mine, Sheldon, owned a ‘66 Mercury Comet Caliente’ with a 289 V8 engine. He drove the car 200 miles a day, five days a week for his work, so he maintained the car according to the severe service schedule. When I met Sheldon the car had 120,000 miles on it and the engine had never been opened up. This was unheard of back then.

Most cars at 50,000 miles had at least the cylinder heads removed and a valve job done. I observed Sheldon meticulously maintained his Comet. Every one to two months or 3,000 miles without fail, he brought the car in for an oil and filter change. Sheldon had to eventually let the old car go because of body rust (with the engine still running like a clock).

He donated it to me so I could perform an autopsy on the engine. I needed to know why and how he was able to log so many miles. Once opened up, the engine spilled its secrets. Internally, it was almost spotless. There was hardly any evidence of internal wear. Vigorous and diligent maintenance had cheated “engine death from sludge,” the most common killer at that time. As a young impressionable mechanic I became a believer in vigorous maintenance.

‘Til next time … keep rollin’.