Soot Patrol Keeping Out That Enemy of Diesel Longevity With the Right Oil
Written by Steve Temple Photos by Steve Temple and Courtesy Shell Rotella
Although all diesel engine oil turns black, it should still remain relatively clean if it's doing its job.
When soot is present to excess, it's obvious. Notice the sludge that's accumulated in the oil pan. This clumping is a sure way to shorten engine life.
When draining the pan some mechanics prefer the oil to be warm so it flows out smoothly, while others like it to be cold so all the oil has already settled to the bottom. Either way, remove as much of the old oil as possible before adding clean, fresh oil.
Removing the filter on a 12-valve Cummins in a '96 Dodge Ram.
If you were to pick out the single most important reason for using the correct type of oil in your diesel engine, it all boils down to one word: soot. You know, that yucky black sludge that's left over from the combustion of fuel.
Other than looking gross, what's the problem with soot? When tiny soot particles clump together, they become abrasive. And when they accumulate, parts rub against each other, which can increase wear and damage engine components.
Soot can also prevent the oil's anti-wear additives from protecting critical parts. It thickens oil as well, which can reduce power and fuel economy, and degrade cold-temperature flow properties, making more work for your starting system.
Soot also contributes to the sludge sometimes found on valve decks and in oil pans, as well as carbon and varnish deposits on pistons and ring grooves. These deposits undermine oil consumption control and can lead to premature engine failure.
Modern diesel engines are even more susceptible to soot damage because of tougher emission regulations that require methods such as exhaust gas recirculation, which add to the amount of fuel soot that stays in the oil.
So how can you minimize the negative effects of soot, other than by regular changes with fresh, clean oil? The key to handling soot is to keep it from forming particles big enough to cause damage.
That's where the choice of the proper diesel oil becomes especially important. Don't skimp on quality oil, because it's one of best ways to ensure long engine life. Start by selecting an engine oil that meets the American Petroleum Institute (API) classification for your engine.
For newer light-duty trucks with a diesel engine, the latest API service category is API CI-4 PLUS. Older trucks may use previous API categories such as CG-4, CH-4 and CI-4. However, CI-4 PLUS supersedes these categories and will provide the highest performance available. Check your owner's manual to get the proper API classification for your vehicle.
Why is the correct type of oil so important? Diesel engines require motor oil formulated with special dispersants that prevent the formation of the clumps of soot. Premium diesel oil helps keep fuel soot finely dispersed to prevent viscosity increase. In addition, it also includes extra detergents and anti-wear components. Using the highest quality oil designed specifically for a diesel engine will provide the most protection and be able to handle demanding conditions such as towing, performance, and off-road conditions.
Some dispersants do a better job than others of keeping soot from becoming abrasive and causing wear. And if not selected properly, detergents and dispersants can actually increase piston deposits and attack seal materials. While there several good diesel oils on the market that meet the stringent API standards, one example is Shell Rotella T. It has special dispersants that help keep the tiny particles from clumping and forming abrasive deposits. Think of it as a way of keeping the arteries clean in your engine's circulatory system.
According to Stede Granger, OEM Service Manager for Shell Rotella, rigorous testing of Shell Rotella T in heavy-duty trucks that log millions of miles has shown that it is able to withstand grueling conditions. Not only that, in our own informal testing on a one-ton '96 Dodge Ram powered by a 12-valve Cummins, we found an immediate increase in fuel efficiency of a mile or so per gallon after just one oil change. That's evidence of how fresh, high-quality oil can get rid of sludge that interferes with engine efficiency.
In addition, premium engine oil goes beyond the basic performance requirements. Not all oils that meet the API CH-4 PLUS standard do what a premium oil does. For example, oil that maintains its viscosity is very important to the overall health of your diesel engine. Multi-grade oils rely on an additive to provide good high-temperature viscosity. If some of that additive is "damaged" or changed in character, oil loses some of its viscosity, and oil pressure drops. This additive damage is called "shear", meaning the additive molecule has been sheared, or reduced in size so that it is less effective in keeping high temperature viscosity where it should be.
Formulating oil with a shear-stable additive means oil pressure is more constant, avoids viscosity breakdown and the oil doesn't have to be designed to start with a high viscosity.
Finally, choosing the base oils that make up the bulk of engine oil is critical. Base oil isn't there just to carry additives. It has its own performance properties, such as solubility, and better oxidation stability, so it can handle extreme heat. With the right dispersant additive, some base oils do a better job of keeping soot and other combustion by-products in the oil, not on engine parts, which after all, is the whole mission of your soot patrol.
Troy from Collins Diesel Injection likes to take a quick whiff of the old oil to check for any excessive burnt odors, which might indicate an engine problem.
Feeling the used oil for any grit or clumping is also a telltale test for potential engine wear.
Fill the new filter with fresh oil before installing it on the engine in order to ensure plenty of lubrication on start-up.
Troy likes use red grease on the filter gasket, but clean engine oil can also be used to ensure that it goes on smoothly and seats properly.
Inspect the plug for the oil pan for any damage to the threads or gasket, and apply lube before reinstalling.
Don't over-tighten the drain plug, or you may run into some other problems.
A funnel helps avoid messy oil spills. Fill to recommended manufacturer capacities then check the dipstick to be sure you have added the correct amount of oil.
If the oil is dispersing the soot, the piston should look more or less like this one.
Soot also contributes to that carbon and varnish deposits on pistons and ring grooves that can degrade oil consumption control, and also lead to premature engine failure.
Sources Shell Rotella www.rotella.com
Collins Diesel Injection 845 S Commerce St Stockton, CA 95206 (209) 948-4410
