Bottom Line
Modern Trucking Techniques
Grime busters

By Paul Abelson
senior technical editor

Truckers today enjoy more time between oil drain intervals thanks to advances in engine and oil technology.

But, all the technology in the world is no match for the gook and grime that builds up over time, eventually killing the effectiveness of your oil – if you leave it unchecked.

Oils and engines have gotten so much better that some engine makers now recommend oil drain intervals of 25,000 to 30,000 miles. It’s mind-boggling when you think about it. Most older engines on the road have recommended intervals of 12,000 to 15,000. Yet, today’s engines must handle more soot and still have intervals nearly twice as long.

Since oils are so much better, you have to wonder what it takes to extend preventive maintenance and drain intervals on older engines.

Today’s oils have improved additive packages. The chemicals suspend more soot, in finer sizes than ever before. If for no other reason, 10-year-old and older engines can safely extend oil drain intervals, even if only for another 3,000 to 6,000 miles.

Extending intervals involves more than just waiting longer to change your oil. It requires establishing an oil analysis program and possibly adding a bypass filtration system.

Engine makers establish recommended intervals to protect themselves from claims during the warranty period. The intervals are generally based on moderately severe duty cycles.

Recommended intervals are conservative. If something does go wrong, the first thing manufacturers check is the service record. If maintenance has been skipped or extended without a basis for doing so, warranty claims will be denied, at least initially.

Know your oil’s enemy
The first tool for extending your drain interval is oil analysis. This is not only recommended by the Technology & Maintenance Council’s Recommended Practice 334, but also in RP 318, which discusses oil analysis and how to use it.

Oil analysis tells you the condition of your oil. It detects contaminants, determines the overall condition of the lubricants and gives you a peek at component wear within your engine.

Simply, oil analysis tells you all about your oil’s condition so you can make the best decision on how long to go between oil drains – and not void your engine’s warranty.

A few years ago, a friend had an engine part fail after 400,000 miles. He had paid for a 500,000-mile warranty with his new truck. The truck had a bypass filtration system that allowed him to change oil and filters at 60,000-mile intervals.

The engine maker claimed he voided the warranty by going so long between oil changes. The OOIDA member brought in his stack of oil analysis reports, done at 15,000-mile intervals over the life of the truck. Each one indicated the oil was in good condition and had ample life remaining. The engine maker covered the repairs to the engine.

While oil analysis will give you an enormous amount of information about your oil, when you’re establishing extended drain intervals there are two key elements to keep your eye on.

You should track the total acid number – TAN for short – and the total base number – abbreviated TBN. The total acid number is a measure of how much acid from combustion is in the oil. The total base number indicates the “base” or alkaline strength of the oil additive package that neutralizes acids. The total acid number must never exceed the total base number.

Once you have two oil analysis reports, you can start a graph of the progression of the total acid number and the decline of the total base number. Use the vertical axis for the TAN and TBN and the horizontal axis for the total miles on the oil.

Unless something catastrophic happens inside the engine, the progression is relatively steady. Continue to chart the progress each time you get a new report. Project the lines, and make plans to change oil before the two lines cross.

A helping hand
Any filtration removes some contaminants so they don’t circulate with the oil. Inside the engine, contaminants grind surfaces where moving parts are separated only by a thin film of oil.

All oil needs to be filtered, but if the filtration is too fine, flow will be constricted. Primary oil filters, called full-flow because all the oil flows through them, capture particles as small as 25 microns. A micron is one-thousandth of a millimeter.

Soot is formed during combustion. Particles start out in the sub-micron size range but grow because they stick together, which is referred to as agglomeration.

The particles grow as large as or larger than clearances inside the engine where they scrape the metal surfaces. Wear metals enter the oil and flow through the engine. The soot and wear metals then increase the abrasion until particles become large enough to be captured in the full flow filter.

Bypass filters capture smaller particles, but because of the restriction caused by fine filtering, only a little oil can flow through those filters at a time. Oil is diverted from the main flow of oil, filtered, and returned directly to the crankcase. It “bypasses” the engine, hence the name.

Bypass systems use very dense filters such as compressed fibrous material, tightly rolled filter paper, cotton mill waste and a variety of others. Some even use rolls of toilet paper or paper towels.

Depending on the density, the system can remove anywhere from 8 to 10 micron particles down to 1 or 2 microns. By removing soot, wear metal abrasion is minimized. Soot also reacts with chemicals in the oil’s additive package. Removing soot extends the life of the additives, helping to extend drain intervals.

Bypass systems require more oil. Adding a bypass system increases total oil by 20 to 40 percent. So, if all else is equal, a 20 to 40 percent longer drain interval is safe. Factor in the reduction in wear metal and the slower depletion of additives, and intervals can be safely extended beyond 60,000 miles, but only if confirmed by oil analysis.

Some makers of bypass filters claim you never have to change oil again, but they require new filter elements frequently. Over time, the oil that fills the new elements replenishes the additive package. It’s usually the equivalent of a complete oil change every 50,000 to 80,000 miles.

Oil drains can be extended safely, but only with proper planning and constant evaluation. Or, you can change oil according to conservative original equipment manufacturer recommendations.

Either way, regular preventive maintenance will help your engine last a long time.

Paul Abelson may be reached at