Since I have been selling aftermarket performance products, there have always been two questions that every customer asked:  “will it affect my warranty?” and  “will I get better mileage?” For sure, both questions are valid and both were answered as completely and honestly as possible with what information we had. However, since the emergence of ultra low sulfur diesel fuel (ULSD) some years ago increasing the productions costs of diesel and the recent cost of a barrel of oil escalating, the latter question seems to be asked first now. In fact, a number of our customers specifically call us and inquire about something, or anything to improve their fuel economy.

   Earlier this year, we actually had a meeting with our sales staff specifically addressing the “mileage gains” question and how to answer it. We were really trying to come up with a generic answer based on all the information that we accumulated throughout the years about fuel economy but kept asking ourselves, “how do we really know?” The last thing we wanted to do was give inaccurate information just to make a sale.  We always felt we could honestly help our customers achieve better fuel economy with the products we carry. All the data we collected up to this point was based on manufacturer information, real-life customer testimonials, and personal experience. But the question still loomed of  “how scientific and accurate was it really?” We looked to some other sources for answers with the intention of answering some of our own specific questions.

   If any of you read the forums, you’ve undoubtedly seen the same responses to the mileage questions that I have. Forums are what they are and you have to scrutinize what you read on them. While I generally view the forums as helpful and a great tool for information sharing, we have all seen a lot of misinformation, myths and utter nonsense propagated on some forums and as such I judge the information accordingly. So where do we get the most accurate information regarding fuel economy gains via aftermarket products? You’d think that the major manufacturers that we represent in our industry would have done the necessary testing to make such claims in print, and to be honest; most customers have backed up those claims almost exactly to the numbers. A few of the most prominent manufacturers that we represent conduct all of their testing in-house. They conduct a base line test with the stock vehicle, and then dyno the vehicle at different stages of mod upgrades and at various rpms, all while recording the data. Once the dyno results are collected, they road test the vehicle in real world scenarios and record those results. The claims that they make in their advertising are usually an average of the lower numbers that they achieved at a given set of parameters. You could certainly make the argument that their results are questionable and maybe even biased but ultimately, the consumer has attested to these claims nation wide. Believe me, we at XDP have collectively spoken to literally thousands of consumers about this topic, and an overwhelming number of them attest to fuel economy gains. Some consumer claims are significantly better than those of the manufacturer but we are typically skeptical of those claims and do not consider them the norm. As such, we usually do not relay them as to be reliable, typical and reasonably expected.

   The government, specifically the Federal Trade Commission, is charged with monitoring posted fuel economy gains used in product advertising. Their concern is not whether it actually improve fuel economy or not, but rather is the advertising a “deceptive marketing practice”. I am neither an engineer nor a statistician and it has been a long time since college chemistry class conducting proper blind and double blind experiments. That being said, we fully believe and trust that the manufacturers have tested and monitored their products in a sufficient manner before making any claims about reasonable fuel economy gains. We further believe that their claims are based on measurable and repeatable tests providing measurable and repeatable results and therefore have no reason to doubt the data. Again, our extensive positive customer feedback has contributed to us accepting the manufacturer’s claims as reasonable.



   The tricky part of answering an mpg question is and always has been explaining it on multiple points. The simple fact is that it’s not that simple. There are a number of factors that determine fuel economy and you have to consider all of them. Unless you realize and scrutinize the facts, you may find yourself fooling yourself. Desperate to do the right thing you may become paralyzed by indecision because of all of the information and misinformation out there. Or worse, you have done something, the wrong thing. Let’s get back to basics.

   First, is the pure technology of how a diesel engine works. Simply put, horsepower is created by burning fuel. But you don’t need to necessarily send more fuel into the cylinder, rather burn more of what you already injected more completely. How and why these performance modifications can produce more power and get you better mpg is simply a matter of getting the engine to combust fuel more efficiently. Essentially, most tuners and other electronic modules enable you to burn more of the fuel more completely during the combustion cycle. In essence, you no longer need to have the engine at full throttle to achieve the desired pulling or acceleration results.  Typically, this means that timing, fuel pressure and injector pulse width are altered. The ECU may be reprogrammed, re-mapped or even “fooled” via simple programming or “data interpretation” to safely and effectively attain these results. Another major engine factor is how efficiently the engine breathes. Getting cooler air in, and as much as you can, as well as purging hot exhaust gasses out is something that is quite easily achieved by the use of a cold air intake system and a better exhaust system respectively. This being the case, it’s no mystery that these three product lines have been the preeminent modifications made to the modern day diesel pickup truck over the last five to ten years. It doesn’t stop there though. Upgrades to turbo charging systems, intercoolers, adding methanol injection, and even improving the transmission also help get the power to the pavement without adding more fuel. Some mods are more expensive than others and the mpg per dollar does go down as you add some of these items but the vehicle is operating more efficiently and if you are towing, they could be a must.

   The second factor is the condition of the engine or vehicle itself. Many customers have called us right after purchasing their diesel truck and are irate over the fact that they just paid an additional $6000.00 for the diesel upgrade over gas and claim they are only getting 8 or 12 mpg. (If you’d like to respond to our mpg poll, click on the following link). What most of these people forget is that the engine does have to break in to get the mileage that they thought they were going get. We usually see this number normalizing at around 5000 miles or so. Conversely, we see customers with over 150k miles on their truck, and it needs basic maintenance to get back to running optimally. Regular oil changes with the proper engine oil, injection system service, fuel filters and some type of trans service are usually needed at this point. Despite what many people think, a diesel engine is NOT supposed to blow black smoke. Sometimes the smoke is due to engine wear and tear or neglect and sometimes it’s because of a mod the owner made. If it’s the latter, the mod was either not installed properly or more mods need to be made to complement the upgrade or perhaps it’s simply not a quality product. A diesel engine will not flood like a gas engine, it will simply try to burn as much fuel as possible, a function of compression, timing and air, and then purge the rest on the exhaust stroke. While working on fuel injection systems for heavy-duty trucks, I spent countless hours at a hot and noisy test stand to make sure that injection pumps were calibrated perfectly and within spec. Over fueling is simply a waste of fuel and ultimately, money. I used to tell truck owners, “if you see black smoke coming out of your exhaust, those are dollars in the form of wasted fuel”.  The short answer to this point is do the right mods that match your intended vehicle use and maintain the vehicle. Choosing the right mod is something that requires you to ask yourself some questions and consulting a knowledgeable source. We at XDP have had our sales staff trained by most of the manufacturers that we represent so we can give the most complete and accurate advice. I don’t know of many other companies who sell diesel performance products who can make that claim.

   Lastly, there are the other “miscellaneous” forces that effect fuel economy. Ultra low sulfur fuel, for instance, does not have the cetane level that the fuel of years ago had. It simply does not put out the same power per charge because of the shorter time between injection and combustion. Additional forces including tire size and condition, air temperature, altitude, where you drive, and the load on the truck all have to be accounted for as well. Another important fact for us at XDP to consider is the buyer’s expectations and whether they are realistic or not. But the most important thing is at the end of your right leg, your foot. Heavy and fast acceleration will burn the coal quicker than anything you can do to counteract it. There are customers that did not see any gain or maybe even a reduction in mileage after purchasing a product that claims to increase mileage, I often question it. Not that I don’t believe the customer but I question why. I wonder what went wrong, because too many people have had positive results. I wonder what is it about their vehicle or their particular set of circumstances that led to undesirable results and ultimately dissatisfaction.

   I’ve just listed most, but not all, of the things that we take into account when consulting on the topic of fuel economy and mileage gains and it’s important that we recognize each and every one of them. There are two points to be taken into consideration when thinking about selling something for fuel economy, the undeniable physics behind fuel combustion and vehicular motion as it relates to fuel economy and the ethical issue of being honest with the consumer. We at Xtreme Diesel acknowledge both and thus try not to make promises on mpg or give exact numbers. That’s the point of this article; while it’s probable you will see some mpg increase, it’s just not that easy to make such a claim as to an exact number of increased power or mpg if you buy any particular product. Even the manufacturers make disclaimers as to reasonably expected increased fuel economy numbers. We instead suggest the items that will most likely do what we all can reasonably expect them to do. Usually, installing complementary mods that work with the vehicle as a whole is the most effective method. Also important is recommending modifications that are going to achieve all the goals that the consumer desires. The high cost of fuel affects us all in one way or another. The good news is that there are affordable ways that are proven by manufacturers and your fellow diesel truck owners alike to improve the fuel economy of your diesel truck. Fuel economy can absolutely be increased but it is ultimately up to the driver to make sure they do all the things necessary to achieve this goal and to be realistic in their expectations.