Maintenance Q&A
Delivering a diagnosis

By Paul Abelson, senior technical editor

Q. You’ve written before about dealers adding imaginary problems to make work and pad their bills, but this one really gets me. I have a 2010 International Lone Star with a MaxxForce motor. It doesn’t use SCR.

Lately I’ve been having problems with the DPF (diesel particulate filter) clogging up, and it uses way too much fuel (in my mind) to do a regen. I had the DPF taken off the truck and cleaned at about 250,000 miles and the engine computer says it needs it again. I have barely more than 150,000 since the last cleaning. And to make matters worse, the dealer wants to sell me on rebuilding the turbo.

What in heaven’s name does the turbo have to do with the DPF? Is this another dealer rip-off?

A. If you follow what occurs in the Advanced EGR process that Navistar used with their MaxxForce engines, the turbo could be a definite part of your problem.

When a turbocharger starts to wear, its bearings usually wear first. Oil cools the turbo as well as lubricates it. If the engine is shut down before the turbo is cool enough, oil stops being pumped. On the hot side of the turbo, the oil sits in the bearings and starts to bake.

Metallic compounds form ash that cannot be dissolved. The ash scratches and scuffs the bearings as it is flushed away when the engine restarts. Much of the ash is trapped in your oil filter, but particles finer than 25 microns (about 0.001 inches) continue to flow in the oil, accelerating wear with every pass through the engine and turbocharger.

Some of the ash and soot particles get into the air intake stream. Since ash does not burn, it goes through the combustion process and gets added to the exhaust flowing into the DPF. More ash enters through the combustion of the lubricating oil that coats cylinder walls and flows past valve guides. The amount is microscopic at each incident, but assuming you average just 1,400 rpm when you drive, you will have racked up 210 million engine revolutions in 150,000 miles, or 630 million combustion events.

Soot is burned off when your DPF regenerates and converts it to carbon dioxide and water vapor. The process is controlled by pressure sensors that measure how much back pressure is in the DPF. The more it is loaded with ash, the greater the back pressure.

A good technician, like a good doctor, is taught to find the underlying causes of a condition, not just to treat the condition itself. By finding that your turbo is leaking, your technician probably found the reason why your DPF was regenerating more often, and why the computer wants it cleaned out 100,000 miles sooner than before.

Q. What is your opinion on oil bypass filtration systems and extending oil changes? One company I talked to wants you to replace only their filter at regular service intervals and not the main filter. They also say not to change the oil unless oil analysis says to. I’m from the old school and also run an old-school engine, Cat 3406B, and this seems a little extreme to me. I feel that the main filter should be replaced at least every other interval. Also, should I switch to synthetic oil?

A. Back in the mid-1990s, I helped write a Recommended Practice for The Maintenance Council, RP334, Guidelines for Establishing Proper Oil Drain Intervals for Heavy-Duty Diesels. Since then, TMC has added “Technology” to its name and the RP is currently being updated for the third time.

I am a believer in bypass filtration. However, since Cat switched from 3406B to 3406C before the RP was written, yours is a fairly old engine. I am not sure that the cost of adding a good bypass filter would give you the payback you would expect before the engine wears out. It must be getting close to the end of its useful life, unless it has undergone a recent rebuild.

In our last issue, I answered a question about Gulf Coast and other bypass oil filters. The questioner’s engine was less than two years old. I recommended bypass filtration for his newer engine, but yours is a different situation. If you plan on extending your oil drain interval, verify that your oil is still good using oil analysis.

With a new engine or a remanufactured one, I would definitely recommend both bypass filtration and synthetic oil, but not for a 20-plus-year-old engine.

However, engine oil chemistry has improved greatly in the past 20 years. Detergents, dispersants and other components have changed since we no longer have to contend with acids formed when diesel contained as much as 3,000 parts per million (ppm), or 0.3 percent sulfur. Your engine may have been put in service before mid-1993 when the switch to low sulfur diesel (500 ppm) began. Since 2006, ultra-low-sulfur diesel has contained only 15 ppm. That changed the chemistry of combustion, and oils have changed accordingly.

As for fully synthetic oil, it will help you extend drain intervals eventually, but since it is naturally more detergent than mineral oil, you can expect your oil to carry much more dissolved soot and sludge than before. Expect your filters to clog much sooner. It may take two oil drains or more, each at 5,000 miles or so, to get rid of the accumulation. That would negate any advantage you would gain with synthetic oil.

If you plan on extending your oil drain interval, verify that your oil is still good at each decision point using oil analysis. LL


DO YOU HAVE A maintenance question?
Send your question to Paul Abelson, senior technical editor, in care of Land Line Magazine, PO Box 1000, Grain Valley, MO 64029; email them to or fax questions to 630-983-7678. Please mark your message Attention: Maintenance Q&A.

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