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Modern Oils
The majority of operators take their trucks in for new oil at the intervals recommended in the owners' manual. Most specify brand of oil, but that's it.

But there's more.
Oil contributes as much as one third of an engine's cooling, so shouldn't you know more?

by Paul Abelson, technical editor

For most owner-operators, changing oil is just something to be done regularly, so they take their truck to a dealer, service shop or truckstop. Most then choose a level of service from a posted schedule. Basic service includes new oil and filters. More expensive services involve additional inspections and services, but the oil change remains the same. Usually, you get up to 11 gallons of one of the premium oils, although some shops base prices on a standard grade oil, and upcharge for oils like Delo 400, Delvac 1300 and Rotella T. And for considerably more money, you can get synthetic oils like Delvac 1 or Royal Purple Long Rider.

The majority of operators take their trucks in for new oil at the intervals recommended in the owners' manual. Most specify brand of oil, but that's it. That type of maintenance works well, as long as you stick to factory recommended oil drain intervals. Factory recommendations are conservative. They have to be to protect warranties.

Drivers can and do extend intervals, often many times the original recommendation. They use additional filtration to keep the oil clean and premium or synthetic oils to maintain oil characteristics. They also use oil analysis to determine how effective the oil is. By plotting successive readings on a graph, smart operators can predict how long their oil will last. Some oil analysis labs will even graph and plot your results. Even though reports come back with good readings, many owner-operators set their own arbitrary limits.

If you plan to extend drain intervals, oil analysis is imperative. Here's a story that illustrates why: Members Mike and Gail Swiger's Pete has a Detroit Series 60 engine. They use Amsoil synthetic oil and a Como ( bypass filter. They do analysis regularly, but choose to change oil around 60,000 miles, even though the reports come back that the oil is good for tens of thousands more miles.

A while ago, with the engine nearing the end of its warranty, a con-rod bushing let go, putting metal fragments into the oil pan. Mike and Gail took the truck in to their Peterbilt dealer who filed a warranty claim. When he learned that the oil hadn't been changed for 58,000 miles, the Detroit Diesel rep denied warranty. Mike confronted him with a stack of oil analysis reports and asked, "Which one of these says my oil is no good?" The Swigers got their engine repaired under full warranty.

"What oil should I use?"

As a technical editor, I often get asked, "What oil should I use?" and "Should I switch to synthetic oil?" The answer is always the same: "It depends." To answer those questions, it helps to have an understanding of what oil is and what it does. We tend to think of oil as a slippery liquid that, somehow, comes out of crude petroleum. Being slippery, we use it as a lubricant. True, but that's only part of the story.

Oil lubricates, reducing friction between parts that slide or rotate. It also cools and cleans the insides of our engines. Burning diesel in the combustion chamber releases energy that pushes the piston down to power the vehicle. Some of the energy, released as heat, is absorbed into pistons, cylinder liners, cylinder heads and valves. They are lubricated by oil, and as the oil flows away, it takes some of the heat with it back to the crank case, to be lost to the surrounding air and to the oil cooler. Oil contributes as much as one-third of an engine's cooling.

Oil seals, filling the spaces between piston rings and cylinder walls, and between valve stems and valve guides. The oil prevents gases from blowing through any voids between them. Oil cleans by carrying detergents and dispersants to where soot and sludge form.

When diesel burns, there is always a residue of unburned or incompletely combusted fuel. We call it soot. With emissions regulations forcing the issue, engine makers learned how to reduce (but not eliminate) the soot made during combustion. They also learned how to keep it from blowing out the stacks. They trap it with engine oil and let the oil carry the soot into the crankcase. Incomplete combustion creates additional contamination, especially before the engine reaches full operating temperature. Left alone, sludge and varnish are deposited in the engine. Oil controls the soot, sludge and varnish.


To do these tasks under the thermal pressure and chemical stresses an engine is subjected to takes a good deal more than just oil. Chemical additives make up as much as 35 percent of what winds up in your engine's crankcase oil.

  • Anti foam agents break up air bubbles, so a full charge of oil goes through the oil pump into the engine.
  • Antioxidants retard the oil's breakdown due to the air.
  • Anti wear additives prevent rust.
  • Detergents dissolve sludge and varnish.
  • Dispersants keep soot and other contaminants from
  • depositing on internal surfaces.
  • Extreme pressure additives keep lubrication on parts that have small, highly stressed contact area, such as gear teeth and cam lobes.
  • Friction modifiers help keep the oil slippery under adverse conditions.
  • Viscosity improvers extend the operating temperature range for oils, giving the oils more body when hot.

As you can see, oil formulation is a complex subject indeed. It is made more so by the changing demands placed on oil as engines become cleaner to meet EPA regulations. Not too many years ago, CD oils were created to meet the demands of early turbocharged engines. They could safely suspend about 1 percent of their weight of soot. As oils were called on to carry more soot, engine makers worked with the American Petroleum Institute (API) to raise requirements and develop tests to prove that the new requirements were met. Every time API changed the oil requirements, the designation changed. From CD, we went through CE, CF-4 (the breakout for 4-cycle engines vs. 2-cycle), CG-4 and now, CH-4. The latest, CH-4+ (plus) can suspend up to 7.5 percent soot and still resist wear under extreme conditions.

Engines are designed to use oil with a specific set of properties. The newer the engine, the greater the stresses and the higher the designation of the oil required. If an engine was designed to use CG-4 oil, it may run better on CH-4, but it will wear out sooner than it should if you use CE or CF-4.

So, getting back to the question, what oil should I use? Any oil that meets the specifications called for by the engine maker and changed according to recommendations. All oils designated CH-4 meet the same minimum specifications. Does any one do it better? I doubt it, but some do it longer and provide a greater safety margin. That is the true difference between the popular premium oils and the CH-4 oil available from mass marketers under private brand. One exceeds the requirements, while one may just meet the requirements.

Like mineral oils, synthetics also have a significant volume of additives. The differences are in the base stocks used. A base stock is the oil used to blend with the additives. Mineral oils contain impurities and sulfur that cannot be completely eliminated. Even the best mineral base stocks have mixtures of various sized molecules, giving varying properties when exposed to temperature extremes. Recent improvements in refining base stocks, such as hydro-treating (or reacting with hydrogen) yield improved base stocks. But for lubrication engineers to have the greatest control over oils' properties, they synthesize (or create from other materials). These synthesized (or synthetic) oils are made from natural gas, coal gas and some liquid hydrocarbons. Engineers are able to cut heavy molecules apart to make lighter ones, and to splice light molecules together to the exact specifications desired. Synthetic oil is uniform, with no heavy molecules to thicken in the cold, no sulfur to contribute to pollution and no natural impurities to affect performance.

The benefits to operators who use synthetic oils are that the oil has better thermal properties and longer life. Because its molecules are uniform and free of wax, the oil flows easily in extreme cold, yet will not break down or vaporize under extreme heat. While mineral oils turn thicker and thicker as lighter fractions cook off, synthetics maintain their designed properties longer. And because they are free of heavy fractions, sulfur and other impurities, they start out cleaner in your crankcase and stay cleaner longer.

If there is value to staying on the road longer, you can extend drain intervals by using synthetic oil. But unless you intend to go 50,000 miles or more between oil drains, or travel in extremely cold climates, synthetic oil may not be worth the extra price.

The questions were: "What oil should I use?" and "Should I use synthetic?" The answer remains the same. "It depends." But now you know upon what.