Miles Per Gallon is currently the biggest topic in the Diesel truck owner community. From over-the-road tractor tailers to daily commuters with mini-diesels every one is noticing the impact of high fuel costs right now.
The reality is, you're never going to get 30 MPGs with a full-size diesel pickup truck. That doesn't mean there's no hope for better than average though. In real-world conditions, our experience has been that you can expect somewhere in the high-teens for MPGs from a 7,500-8,500 lbs truck.
Here are the most important things you can do to get the best possible MPGs from your Duramax, Cummins, or Power Stroke.
This should go without saying. However, we have come across a surprising number of HD truck owners that don't know they have an underlying mechanical problem. So many problems with your truck can start slowly and go unnoticed for a long time. Something like a boost leak, or underperforming CP3 pump, can take months to get bad enough for you to notice.
Boost leaks specifically are notorious for slowly draining efficiency. Your diesel relies on compressed air being pushed by the turbocharger into the engine. The system of pipes and parts that connect the turbo to the combustion cylinders is called the Charged Air System. Any leaks within this system can wreak havoc on your MPGs.
In a best-case scenario, we see common rail diesel engines pick up 2-4 MPGs after tuning. This would be driving around 60 MPH, on flat ground, with a tail wind, at sea level, in a truck with perfect health, and stock tires. When you can use the added power from custom tuning to run a higher gear you’ll be using less RPM to do the same job. Reasonable drivers often report 2-3 MPG gains in unloaded, mixed driving scenarios.
Big tires, heavy bumpers, and excessive lifts are often the culprit to unreasonably poor fuel mileage. If you don’t have those problems, often a boost leak within the charged air system can cause excessive smoke and bad MPGs.
The bigger and heavier your wheel and tire combo are, the worse your fuel economy will be. The added rotational mass requires more fuel to produce the same power. 35” tires on a reasonable rim seem to be the limit before a steep cliff in efficiency.
You will never get the same MPG while towing as you will be unloaded. The weight and wind drag created by your trailer, and the health of the truck make a big impact on MPGs. The best strategy to improve your towing MPGs with tuning is taking advantage of “Shift Up, Throttle Back”. The added power and wider torque curve are there to find a speed that allows you to run a higher gear than usual, thereby using less RPM/Fuel to do the same job.
If you cruise at 90 MPH on the highway there isn’t much that can help you on fuel mileage. We have documented our biggest gains in efficiency on 2 lane highways doing around 60 MPH. The extra power from custom tuning will give you the get-up-and-go you want when you need to pass someone and take advantage of a more responsive throttle pedal when you need it.
Your transmission computer (TCM) calibration is based on the expectation of stock torque outputs and throttle pedal inputs. Upgrading to custom TCM Tuning from Calibrated Power means matching your TCM tune to your ECM tune. This prevents clucky shifts and hunting for gears, which cost you MPGs, and massively improves your driving experience.
Make sure your truck is in sound mechanical shape. Include a boost test to your maintenance schedule. Avoid modifications the drain efficiency. Use custom tuning from Calibrated Power as a part of a “Shift Up, Throttle Back” strategy.