3 Upgrades to Add 5MPG to Your Diesel Truck

As much as we love diesel trucks, the poor gas mileage is one of the biggest downsides. Fortunately, there are a few upgrades that can actually help you get up to an extra 5 miles per gallon. While the mileage increases will depend on what diesel you have, you can still expect anywhere from 2-5mpg improvements from just three modifications.

In this article we're going to cover 3 upgrades to help boost gas mileage: tuners, cold air intakes, and exhaust systems. Furthermore, we will discuss a few a popular upgrades that you shouldn't do that actually decrease fuel economy. Lastly, we will do a cost breakdown analysis to show you the payback period it takes to recoup the cost of the upgrades.

Upgrades to Increase Diesel Gas Mileage

1. Tuner / Programmer
2. Cold Air Intake
3. Exhaust System

Out of the three upgrades on the list the two most beneficial are going to be tuning and an intake. Exhausts will provide some benefits but they have the longest payback period as we will discuss below. There are a few other upgrades that are great like intercoolers and differentials, but these things get expensive to the point that the payback period just isn't worth it.

Before we jump in, let's point out a few caveats:

• The gains are going to mostly be seen from highway driving - you likely won't see +5 MPG in the city and instead will only see marginal gains there.
• These upgrades will also add some extra power to your diesel truck. If you go using too much of this newfound power you likely won't see the full benefit.

1) Tuning: +2-4mpg

The biggest fuel economy improvements are going to come from engine tuning. There are tons of routes to go here when it comes to canned vs custom tuning, the various tuners on the market, and the types of tune you run. You're also going to get power gains from a tuner, but you can actually still get both power gains and gas mileage gains at the same time.

Tuning really optimizes the engine and turbochargers efficiency which is where the gas mileage improvements come from. Running a low-power or what is commonly referred to as an "economy" tune you can see anywhere from 2-4mpg increases, with some tuner and engine combinations even providing more.

While custom tuning is a great route to go for maximum benefit, the cost really weighs down the benefit. Custom tuning will typically run $1,200 to $1,500. For those purely seeking better gas mileage, the best route to go is getting a canned tuner which will be closer to the $500 mark and still provide about the same fuel savings.

Here are our tips:

• Canned tuners are best for value and have the lowest payback period
• Custom tuning is great but costs about double, making the payback period twice as long
• Stick to the economy or low-power tunes, running a +100hp tune will decrease fuel economy
• Tuning is 100% worth it for the other added benefits you get too

Shop Tuners and Programmers

2) Cold Air Intake: 1-2mpg

An upgraded intake system, or cold air intake is going to be the second best upgrade to increase fuel economy. An intake will increase air density and reduce restriction. This in term improves turbocharger efficiency, leading to lower EGTs which reduces thermal load on the engine ultimately improving gas mileage.

An intake will provide around 1-2 mile per gallon of improvement. Although, these gains will be most noticeable on the highway with an intake providing minimal fuel economy benefits during standard city driving.

Here are our tips:

• Stick to intakes with high quality filters, avoid the cheap products from China
• Open intakes have bigger airflow increases and therefore bigger benefits
• Combining an intake with a tuner will amplify the benefits of both, they are highly complimentary

Shop Boosted Performance Cold Air Intakes

3) Exhaust Systems: +0.5mpg

Upgrading your exhaust system with a downpipe, downpipe-back, or DPF-back exhaust system will help provide some marginal improvements. These upgrades will reduce backpressure in the exhaust which increases turbo efficiency and lowers EGTs, which also reduces thermal load. However, an exhaust is going to provide the most minimal improvements to the point that it isn't the most worth it based on costs.

Overall, when purely focusing on gas mileage, our recommendation is to skip the exhaust and just do an intake + tuner combination which will get you 95% of the benefit. However, an exhaust upgrade is one of the best things you can do to lower EGTs which improves reliability so it is worth it for the improved engine health caused by lower engine temps and EGTs.

Here are our tips:

• Downpipes have the biggest impact
• A 4" or 5" turbo-back system is the best (if you don't have DPF/SCR/DOC)
• Aluminum exhausts will offer the shortest payback period but might rust in rust-prone climates
• Worth it for the EGT benefits alone

Shop Diesel Exhaust Systems

Upgrades to Avoid That Decrease MPG

If you are focused on maximizing fuel economy, you are going to want to avoid a number of upgrades. Bigger wheels and tires are awesome but they're terrible for fuel economy unfortunately. Here are a few pointers and mods to avoid:

• Bigger wheels and tires
• Lift kits
• Running aggressive or high-power tunes
• Larger injectors
• Other power-adding modifications

Basically, anything you do increase horsepower beyond what we recommend in this list will decrease gas mileage. More power requires more fuel so there is a fine line in tuning and modding between improving gas mileage and actually decreasing it. 

Furthermore, bigger wheels and tires are probably singlehandedly the worst thing that you can do. These add more roll resistance and rotational weight, requiring more power to get your truck going and keep it going. 

Payback Periods

	Tuner	Intake	Exhaust	Combined
Cost of Mods	$500	$300	$400	$1,200
MPG Increase (avg.)	2	1	0.5	3.5
Miles Driven/Year	15,000	15,000	15,000	15,000
Gallons Saved	153	82	42	244
Savings @ $4.00/g	612	328	168	976
Payback (Years)	0.82	0.91	2.38	1.23

As we can see, an exhaust is the least worth it. Also, for calculation purposes, I started out assuming a 12mpg starting point and the combined gallons saved is lower than the sum of all because of the effect of doing all upgrades vs only one. I also assumed an average increase of 3.5mpg since I assume a relatively even split of highway vs city driving.

Summary

The 3 best upgrades for increasing diesel truck gas mileage are tuners, intakes, and exhaust systems, in that order. Performing these three upgrades will add around 2-5mpg depending on your truck and how you use it. These upgrades can be had for around $1,200 for all three if you stick with the budget options which ultimately leads to a payback period of slightly more than one year. In addition to upgrades, there are also a few things to avoid such as bigger wheels and tires, lift kits, and other power-adders.