This is a printed article from, dated June 1996. It is sponsored by Pennzoil Motor Oil Company and that's why there is reference to that product in the article.

I found the article informative for all to read regarding the formation of the dreaded engine sludge that many Toyota owners are finding in their vehicles.


In the last issue I said that mechanics should be called "automotive systems analysts," because the knowledge and experience we must acquire to be good truly earns us that title. I also said the engine's oiling system was an all-important system. In this issue, I would like to take the oiling system discussion a bit further and talk about a topic automotive analysts everywhere will be able to relate to: sludge.

Horror stories have been passed around for years about this motor oil or that motor oil causing sludge. The fact of the matter is that no motor oil causes sludge. In fact, motor oil actually helps prevent sludge.

Then where does sludge come from? In our continuing quest for oiling systems knowledge, I thought it would be good to take a minute and further investigate what sludge is, how it forms, and how to prevent it. I also want to explain how a top-quality motor oil, like Pennzoil, keeps engines free of sludge, deposits and corrosion.

The Sludge Monster

We've all probably taken apart an engine or seen an engine that's been consumed by the "sludge monster." It's not a pretty sight and has been the cause of death of many engines. The first clue that an engine has been inhabited by the sludge monster usually becomes evident during an oil change (when the thick goo dribbles out the oil pan drain hole or nothing at all comes out). We usually identify the fatal cases of sludge monster victims after the vehicle arrives at the shop under the auxiliary power of a wrecker.

Contaminants and Sludge

Contaminants are deadly enemies of an engine. They enter with the air flow and are also generated by the friction of metal against metal. These facts may astound you: for every 100 gallons of gasoline burned in an engine, the following by-products are produced:

90 to 120 gallons of water

3 to 10 gallons of unburned gasoline

1/2 to 3 pounds of soot and carbon

1/4 to 1 pound of varnish

1 to 4 pounds of sulfuric and nitric acid

A measurable percentage of these by-products ends up in the motor oil. Detergents and dispersants in the oil must be able to keep most of these con-taminants neutralized or suspended in the oil as microscopic particles so they don't form sludge, damaging deposits and corrosion. When the waste materials are dispersed properly in the oil, the filter can trap the larger particles. During an oil change, the contaminants too small to be filtered are re-moved with the engine oil. Looks good on paper, right? So much for the perfect world. It's important to note here that good air filters and good oil filters trap more contaminants than lesser quality filters, making the oil's job easier.

Paraffin-based Crude Oils

Most people relate the word paraffin to candle wax. This is a correct association, BUT one of the most incorrect and widely circulated misconceptions about sludge is that it forms more easily in paraffin-based motor oils. This couldn't be further from the truth. All major motor oils, in fact, are formulated using a paraffin-based crude oil. Naphthenic-based crude oils are actually more likely to form sludge in an engine than oils formulated with paraffin-based crude oils. This is due to the higher breakdown resistance of paraffin-based crude oils. O.K., so how does sludge really form?

How Sludge Forms

Sludge formation begins when the chemically suspended particles of contaminants begin to settle out of the oil. It's a fairly daunting task for engine oil to suspend all the contaminants thrown at it, and any engine oil can do this successfully to a point. Pennzoil, and some other quality motor oils, are able to perform this task more effectively and for longer periods of time. But eventually, if the oil is not changed often enough, a "breaking point" will be reached. This breaking point is either when there are too many contaminants to handle or when the oil's chemical defenses are weakened, and it is caused by two main things: excessive accumulation of contaminants in the oil and chemical changes in the makeup of the oil itself (depletion of the additives and oxidation).

As more particles are suspended, less of the additives are available to do their job. Knowing this makes it easy to see why too much time between oil changes can be one cause of the oil reaching its "breaking point".

A Surprise Visit From the Sludge Monster

Another cause may surprise you: running the engine low on oil for a prolonged period of time can cause sludge. The detergent and oxidation inhibitors are important components of the additive package that prevent sludge from forming. When an engine is run low on oil, these additives have to work overtime to do their job. There is simply less of the additive package available to do the work of suspending particles and preventing oxidation (thickening) of the oil.

Here is the surprise part: running an engine just one quart low on oil for about as long as some technicians work in one week (about 55 hours) can increase the viscosity, or the thickness, of the oil by over 1000%!!! I don't know many technicians, or car owners for that matter, who would like to run 5,000-30,000W oil in their car's engine. If you factor the effects of the increasing use of self-service gas stations into the equation, you can see how the sludge monster can unintentionally be invited to pay a visit to so many engines.

Eliminate Surprises

The sludge monster's invitation can be repeatedly rejected. To keep the sludge monster looking for a dinner date in someone else's engine, use a quality oil like Pennzoil, with its super powerful Z-7¨ additive package and change it at recommended intervals. It's like making sure the Kryptonite never gets near Superman.

We're the Automotive Systems Analysts

Our customers look to us to know the various vehicle systems and how they operate. The oiling system is no exception; it's the life blood of the engine. I hope this information adds to your ever-growing base of automotive technical information and helps you to explain motor oil's importance to your customers. Next issue, now that the sludge monster is running scared, we'll take a look at the other additives in motor oil that weren't discussed here. We'll see that the slippery substance is truly a chemical wonder.

* Pete Sullivan is a technician and owner of Sullivan's Advanced Auto Care in Houston, Texas. He is a triple master certified by the National Institute of Automotive Service Excellence (ASE). He holds a B.S. degree in Physics and Chemistry.