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Betting on a Gas:
from Diesels to Cummins CNG Trucks

In mid-2015, FCA US (the former Chrysler) converted their entire fleet of component-delivery trucks in Michigan to compressed natural gas (CNG). They announced key features, costs, and advantages of using CNG, rather than diesel, trucks, but this change was far more than simply swapping engines or tractors; and the advantages were greater than just improved fuel economy and emission levels.


Chrysler/FCA US has 179 heavy duty trucks based in Detroit; they travel across Michigan, Ohio, Indiana, and Ontario every day, moving components between plants. Once Chrysler was freed from Daimler, they used diesel Mack trucks with manual transmissions, but this year the deal with Mack expired. The company jumped from diesel Mark trucks to CNG Peterbilts; the benefits extend beyond fuel economy, but the costs go beyond paying for 179 new trucks.

at the pump

The Headaches of Swapping to CNG

The old trucks went back to Mack, and will presumably be reconditioned and re-sold.

Replacing 179 heavy duty tractor trailer trucks was the bulk of the $40 million investment by Chrysler, but the company also had to add a fuel station and upgrade the Detroit truck depot facility to service CNG trucks.

cummins cng engine

The Peterbilts use 12 liter Cummins turbodiesels with unique cylinder heads and fuel systems to use highly pressurized natural gas rather than the liquid diesel. Most of the trucks are similar to any modern “class eight” truck, so most repairs and maintainance, even of the engines, is similar to normal trucks. Mechanics needed special training to deal with the unique fuel storage and delivery systems, but there were also major safety changes required.

Cummins engine

Compressed natural gas is, well, a gas – while diesel fuel is a liquid. When the Chrysler fleet was using diesel trucks, a fuel leak meant a puddle on the floor which needed to be carefully cleaned up. A fuel leak in a CNG truck can quickly lead to a cloud of toxic, explosive gas — though because it’s much lighter than air, the explosive gas will quickly rise to the ceiling. The company had to go through the ceiling of the repair shop and remove all wiring from the top 18 inches of the room; so if the gas leaked and pool against the ceiling, there would be no wires to possibly ignite the fuel-air mixture.

Cummins engine

For the same reason, the Chrysler parts fleet truck garage doesn’t have a traditional heating system, since that can also cause a spark that can ignite a natural gas leak. Instead, the depot has a fresh air system along with an air monitoring system which constantly checks the level of CNG in the air. Should that level get high enough to indicate a leak, an emergency venting system purges the fresh air system while immediately opening all of the doors and windows — engaging well before the air has reached a point where it will ignite. (Natural gas occurs naturally, and when vented into the atmosphere, it dissipates harmlessly.) Finally, the wall separating the garage from the offices has a thick firewall, just in case there is an explosion or fire from the CNG trucks.


This upfitting of the garage cost the company around $1.8 million.

FCA also installed the largest private CNG fuel station in North America, with both high speed and low speed charging stations. This portion of the CNG upgrade cost around $5 million.

Advantages of CNG Trucks

The company said that the new CNG heavy duty trucks will cost the company around 35% less each year compared to a diesel fleet (including the costs of upgrades spread over the expected life of the trucks) and send less harmful emission gases into the atmosphere, but these new Peterbilts are more than just a fancy fuel system.

The 12 liter Cummins CNG engines are not just more efficient, but have fewer cold weather issues since the CNG does not thicken like diesel fuel. Drivers said that difficult cold startups were a thing of the past.


Each of these 179 trucks has an Allison automatic transmission, which makes driving around town simpler than the older, manual-transmission trucks, keeping the drivers fresher while on the road. Each cab has a power adjustable driver’s seat that is both heated and cooled, for new levels of comfort on long hauls from Detroit to Kokomo, Indiana or the short ride across the crowded bridge to Windsor.

storage tanks

Drivers took pride in their new trucks, not just the comfort — though they talked informally about how much they love their jobs now, as they have the nicest trucks on the road; they all love the gray bodies of the truck and the massive polished aluminum wheels.

Finally, the Peterbilts are packed with modern technology, with a touchscreen infotainment system, radar-assisted cruise control with crash avoidance and blind spot monitoring. The 6-wheel disc brake system works with the safety systems; and there is a backup camera to speed trailer hookups before heading out for a long, relatively eco-friendly work day.


While the costs of the new trucks and their support systems were high, FCA fully expects to earn their investment back — with interest — over the long haul, not just by saving money, but by increasing productivity and reliability.

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