Many people mistake regeneration of a diesel particulate filter with "cleaning" the filter. Although the regeneration process does burn some of the soot 100%, not all materials in diesel exhaust can be burned completely. Materials like fuel additives, oil additives, and bypass oil from rings and seals is what creates ash in the filter.
The regeneration process begins when backpressure builds up, signaling the engine it is time to be "cleaned." At this point, the engine doses raw fuel on the face of the catalyst, which oxidizes fuel and creates heat at nearly 1300 degrees F. Now we've mentioned previously that not all particles in diesel exhaust will burn 100%. This material is what creates ash that remains in the filter.
Ash acts as an insulator within the filter, and the regeneration process only cleans up to the next layer of ash. The only way to eliminate ash buildup over time is by physically cleaning the filter.
So the answer seems simple...clean the filter when the light illuminates on the truck. That concpet works if you subscribe to the "reactive cleaning" approach, and don't mind downtime or increased marginal costs. Below is an example of how a contaminated filter can be costing you hundreds of dollars each month, all happening before the filter light illuminates.
For every 2% a diesel particulate filter is dirty, over 50%, you lose 1% in fuel economy. At 70% contamination, which is generally before the filter light illuminates, you have lost approximately 10% of your fuel efficiency.
Now 10% may not seem like a lot until you look at the big picture. Let's say you truck averages 550 miles per day. And for this example it's on the road 20 days per month. Using an average diesel fuel cost of $1.945 per gallon, at 70% contamination you are spending an additional $339.60 in fuel...per month...per truck. And this all takes place prior to the filter light illuminating to let you know there's an issue.
So the next time you are reviewing annual vehicle inspections, take a hard look at filter maintenance. Getting ahead of the issue can not only reduce vehicle down time, but save you money each and every month.