Install: AirDog And DieselRx Fuel System Upgrades

AirDog_edited-1The fuel system for a diesel truck requires special needs that the gasoline equivalent does not. Additional filtration, and attention to the fuel system on your truck can help prevent problems such as loss of power, as well as hesitations and hiccups, due to fuel starvation, or interruption. For the needs of this particular truck we selected the Pureflow AirDog II-4G Fuel Preporator, and the DieselRx Fuel Sump. These additions will upgrade the existing fuel system in terms of filtration and delivery efficiency.

About The Truck

The test vehicle used was our 2008 Dodge 2500, with a 6.7-liter Cummins diesel powerplant. The truck is largely unmodified, sans an Edge Tuner, and leveling air bags. Our editor Brent is the lucky owner of this immaculate work-horse, and uses it primarily for hauling the toys to the desert, lake, or other recreation destination.

toyoimg_1906rtBrent has lamented to us the tedious task of having to access and remove the OEM water-fuel separator. Located deep inside the engine bay, this vital component to the fuel system is only reachable from underneath, or with the driver side fender liner removed. He recalled consistently throwing away his clothes after being soaked in diesel, during the seemingly simple task of changing the filter. An owner who looks after his vehicles, Brent keeps his tank full of diesel to avoid excess air in the tank harboring water vapor, which would condense and collect in the fuel. Even with such a precaution, diesel fuel is vulnerable to water contamination, and microbial growth. Such intrusions can have serious consequences to the engine’s performance and longevity.

The AirDog II-4G Fuel Preporator


The AirDog Fuel Preporator system is available in three different configurations; AirDog, AirDog II, and the AirDog II-4G. We elected to install the last of the list, the AirDog II-4G is the top of the range and features a unique system to ensure the fuel reaching your engine is as clean as possible.

IMG_1148Featuring a low amperage motor driving a gear rotor pump, the AirDog is not just a replacement fuel filter. The AirDog is a full fuel-purification system in that it virtually eliminates all water, particulate matter, and entrained air from diesel fuel. While you may be familiar with the importance of removing water and dirt from fuel, entrained air may be an enemy you weren’t even aware of factoring into your diesel performance package.

Entrained air occurs as a condition whereby diesel fuel is sloshed and agitated in the tank forming bubbles. These tiny bubbles are suspended in the diesel fuel, and do not rise to the surface of the fuel as quickly as gasoline because of the increased viscosity of diesel. Unable to escape the suction of the fuel pickup, these bubbles are drawn into the fuel system and travel down stream.before-after

Once the air is in the lines, the tiny bubbles begin to congregate and form larger bubbles. Pretty soon a large bubble is formed, an interruption in fuel delivery is traveling towards your injectors. By cavitating the fuel delivery with entrained air you may experience hesitations, hiccups, and interruptions in power. In order to illustrate the impressive action of this filter AirDog engineered a cutaway display proving the effectiveness of the system. Seeing is believing.

Benefits of the AirDog

  • Maintaining correct injection timing
  • Eliminating spray pattern disruption
  • Allowing for a full power stroke and complete burn
  • Increased power output
  • Increased torque output
  • Longer injector life
  • improved throttle response
The AirDog II-4G “is designed to operate at flows and pressures beyond the maximum requirements of the engine. It receives fuel under vacuum from the fuel tank containing entrained air/vapor, particulate contaminants, and unknown quantities of water.” according to the AirDog website. The AirDog removes these contaminants by way of conventional filtration and water separation, but also applies a low pressure vacuum to draw the entrained air or vapor from the fuel, and returns it to the tank. This way the only fuel making it to the engine is clean, and clear rather than foamy, and potentially contaminated.



The DieselRx Fuel Sump


In tandem with our upgraded filtration we decided to install a DieselRx Fuel Sump. The purpose of the sump is to relocate the fuel pickup to the lowest part of the tank. By no-longer relying on the lift pump to remain submerged we can utilize every last drop of fuel in the tank. We are also trading the responsibilities of an electric pump for the the most reliable force in the universe, gravity. The flow of fuel will no longer require suction to draw it from the bottom of the tank, rather it will exit under the force of gravity to our new AirDog.

Machined from aircraft-grade aluminum, and clear-anodized for durability “the DieselRx Fuel Sump provides efficient and reliable fuel delivery.

By working with gravity to pull fuel from the bottom of the tank it overcomes the natural pitfalls of the draw straw -AirDog

    By working with gravity to pull fuel from the bottom of the tank it overcomes the natural pitfalls of the draw straw” according to the DieselRx webpage. Recommended for users of a diesel applications, the fuel sump can maximize the utility of your stock fuel capacity among other benefits, including:
  • Eliminating quarter tank starvation
  • No more pulling or stalling


It should be noted that if you decide to install one, but not both, of these upgrades the plumbing and wiring will be different. Because we decided to install both simultaneously, the two units are plumbed together from the start. The first step of this installation is to make sure you have a minimal amount of fuel remaining in the tank. With the truck on the lift, we turned to the bench for assembly of the AirDog bracketry.

The AirDog brackets and spacer are constructed of a high-strength polymer for lightweight, and easy assembly. No drilling of the frame is required and various hole spacing makes it possible to locate the AirDog vertically where you want it.

A steel u-channel makes up the cradle for the AirDog filter unit, the kit supplies all the necessary hardware to mount the unit neatly. With the brackets all assembled and the AirDog affixed we take the supplied pipe fittings and prepare them for installation into the billet aluminum AirDog body. A little anti-seize on the threads will ensure no gauling takes place between the fitting and body.

Mounting the whole assembly on the frame rail is as simple as choosing a spot, central for plumbing reach, and accessible for service. We decided to locate the filter  in line with the rear edge of the driver’s door on the outside of the frame.  This will make kneeling to change the filters a simple and mess-free job, no more diesel-soaked shirts.



Tightening the bolts down, the physical installation of the AirDog is complete! Changing gears we switched over to the DieselRx Sump. We had to jump between the two kits, installing them simultaneously because when installed in conjunction, they rely on each other for plumbing and wiring routing. The tank was nearly empty when we put the Dodge up on the lift but as is the case with nearly any vehicle some unusable fuel remains trapped in the valleys of the tank.

IMG_1250The next step marked the point of no return! We identified the lowest part of the tank as the area underneath the OEM lift pump and fuel-level sender. This was to the location of our new fuel sump. The next step was to drill a pilot hole, and drain the remaining two gallons of diesel from the tank.

We were aware that the sending unit would be right on the other side of the double walled tank, and were cautious not to damage it as we drilled through the exterior. Once through the plastic layers the diesel began to flow, and flow it did for some time. The viscosity of this fuel was further demonstrated by a smooth consistent stream.

With the last drops of fuel finally out of the tank we mustered up our courage, and broke out the hole saw. Delicately cutting we proceeded in pulsed rotations until finally the saw grabbed and we knew we were through. Prying the small disc out of the hole we de-burred the opening, and wiped it clean of any plastic shavings that may have remained inside.

With our new access we looked to the next step in the installation. Two backing plates include threaded holes for the sump to engage. The kit provides a template for the transfer of drill pattern on to the tank. We drilled the four holes, one on either side of the parting line on each plate.

With the first holes drilled we fed the plates into the opening, and threaded supplied studs into them for alignment. With the plates centered over the hole and aligned for bolt pattern the sump could be mocked in place, and the remaining holes drilled.

Finally, with the alignment studs removed we could install the sump. We applied the massive o-rings in their machined grooves, and assembled the stainless hardware with their respective rubberized lock-washers. The considerable thickness of the o-rings will accommodate for the textured plastic of the gas tank and prevent leaks.

We took care to think ahead, and clock the outlet of the sump to work with the 90 degree fitting included in the pre-made fuel lines. The quick disconnect fitting points straight out the driver’s side for perfect plumbing.

IMG_1376Plumbing became the major endeavor for the remainder of the installation. In order to disable the lift pump, but retain the sending unit, the AirDog supplied wiring harness removes power to the pump.

In order to access the lift pump and modify it for return line adaptation we dropped the tank. With the tank out we removed the lift pump and installed the AirDog return line fitting and internal hose.

The AirDog kit pre-made lines come with pre-crimped connectors for fuel delivery to the filter, engine, and return to the tank via the original location in the engine bay. When using a DieselRx sump the return line must be modified and relocated from the engine bay to the top of the fuel tank. We spliced into the line, and with the supplied push-lock fitting made the connection to the lift pump turned fuel-return.

Under the hood a few fittings must be changed to accommodate the bigger volume fuel lines. Comparing the stock and AirDog fittings we see that when they say this system flows beyond the maximum needs of the engine they mean it!

With the tank on the way back up under the bed we made the final connections with the return line, and wiring harness.IMG_1415

Securing the tank back up in the original straps, all that was left was the satisfying click of quick-disconnect fittings, and some light wiring. We connected all the lines to the AirDog, sump, and engine. The plug-and-play harness makes wiring as simple as a few connectors, a power, and a ground. With the loom routed into the engine bay we connected up the relay box and leads. With everything routed to our liking, away from rotating, hot, or sharp objects — we applied a few zip ties to tidy-up the appearance.

Diesel engines require fuel priming when run dry or when they undergo an upgrade as extensive as this. With the fuel-water separator removed from the AirDog we filled it with diesel before re-installing it. Cycling the key on and off kicked on the AirDog pump pushing fuel up to the engine. After a few cycles the engine started. No leaks, and we were done! The clean appearance makes these parts look like they belong, and the quality materials mean they will last.

We look forward to hearing Brent’s impressions after he has had a chance to give his truck a good run to the desert or lake!

Article Sources

About the author

Trevor Anderson

Trevor Anderson comes from an eclectic background of technical and creative disciplines. His first racing love can be found in the deserts of Baja California. In 2012 he won the SCORE Baja 1000 driving solo from Ensenada to La Paz in an aircooled VW. Trevor is engaged with hands-on skill sets such as fabrication and engine building, but also the theoretical discussion of design and technology. Trevor has a private pilot's license and is pursuing an MFA in fine art - specifically researching the aesthetics of machines, high performance materials and their social importance to enthusiast culture.
Read My Articles

Enlist in the Diesel Army newsletter.

Receive the latest newsletter with the content you love from Diesel Army, directly to your inbox, absolutely FREE!

Free WordPress Themes

We will safeguard your e-mail and only send content you request.

Diesel Army


We'll send you the most exciting Diesel articles, news, truck features, and videos every week.

Diesel Army


We will safeguard your e-mail and only send content you request.

Diesel Army

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

Off road, Jeeps, 4x4s
Engine Tech
Drag Racing

Diesel Army

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • ORX Off road, Jeeps, 4x4s
  • EngineLabs Engine Tech
  • Dragzine Drag Racing

Diesel Army


Thank you for your subscription.

Thank you for your subscription.

Diesel Army

Thank you for your subscription.

Thank you for your subscription.