The Black, White and Greys of the Duramax Fuel Filter - 3

Volume 1 Issue 2 - Diesel Articles

Article Index
The Black, White and Greys of the Duramax Fuel Filter
Let's Blame Fuel Quality
Three Words: Maintenance!
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Three Words: Maintenance!

Just like grandpa said, water is a killer for any diesel fuel system. Now, with common-rail direct injection, preventing water contamination has become even more critical. So maintain that fuel filter and water separator! As mentioned before, GM recommends changing the fuel filter every 15,000 miles or 24,000 kilometers. (2004s and newer with the latest ECM and Instrument Panel software have a filter life monitor that calculates the fuel filter life based on total fuel flow.) And do not overlook the recommendation (and my Grandpa’s lectures) to drain the water separator at every oil change.

The need to replace the filter every 15,000 miles is well illustrated in the samples depicted on the previous pages Take a look at the inner filter media. As you can see, it is normally paper-colored. It starts to plug, from the bottom up, with black asphaltenes. The filter that was changed at 17,000 miles does not show very much unrestricted media left. Running this filter for much longer could potentially damage injectors. The filter that was changed at 10,000 miles shows a fair bit of life left. The filter that was changed when it was absolutely plugged (the engine would hardly run) shows almost no free filter media. In fact, I had to look for a section of the inner filter that did show a bit of color. Not surprisingly, the injectors on the truck that this filter came off of were damaged.

Duramax diesel fuel filter at 10,000 miles

Duramax diesel fuel filter at 17,000 miles Duramax diesel fuel filter at unknown miles

Samples of the outer and inner filter media taken from several filters. The outer media gets completely black, the inner shows it’s original color. (Click on any image for more information and to enlarge)

Take Care of Your Duramax Fuel Filter!

I trust it is obvious by now that any diesel owner needs to keep up proper maintenance on fuel filters. Even the much-improved fuel filters that GM provides today can be defeated if they are left on the truck until a problem develops from restriction. Changing the fuel filter is a much cheaper option that replacing all eight fuel injectors!

There is nothing wrong with having a good pre-filter system. It will provide an extra layer of defense against contamination and water. If you have any doubts about the quality of the fuel you are getting, I would definitely recommend a good water separator and pre-filter system. And it is worth mentioning again that if you run a fuel additive, use one that will help the water separator, not hinder it by emulsifying the water in your fuel!
Personally, I run just the AC Delco Duraguard fuel filter. I use reputable fuel suppliers, drain the water separator at every oil change, and change the fuel filter based on the fuel filter life monitor. (which usually works out to around 15,000 miles depending on idle time and fuel economy) My Duramax runs fine, as do most that have regular maintenance. That lesson that I learned from my grandpa hasn’t changed over the years. In fact, it has become even more critical as engines have gotten much more sophisticated. So take care of your fuel filter!

One More Thing

You might be asking yourself that if the fuel filter is so critical to injector life, why does GM have a special policy warranty on the LB7 Duramax injectors? Though the fuel filters have shown themselves to be the cause of the majority of injector failures, it is still true that some of the materials in the injector could stand improvement, more notably the well known ball-seat erosion issue (covered in the Winter 2007 issue of maxxTORQUE). However with good fuel quality, good filter maintenance and a pre-filter, some trucks are still running on the first generation injectors. For that matter, a few are still running without having a pre-filter. I believe that it is fairly safe to say that the improvements in injector materials were made largely to better handle the less-than-perfect realities of fuel quality and filtration.

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Comments (1)add comment

Mike Malone said:

Disturbed 3 sets, 216000 miles pre filtered from auxillary tank
What about an air dog?? I did not fully understand what you were talking about in regards to fuel treatments, What do you recommend????
December 15, 2013
Votes: +1

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Joel Paynton is an award-winning GM technician who specializes in Duramax fuel systems. He also does custom programming for any GM powertrain. Visit him on the web at


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