Optimize Engine Efficiency Cummins ISX15 Engine

3 Ways to Improve Truck Engine Efficiency

The biggest variable cost for an owner-operator is fuel. In a breakdown of where fuel energy is used on a truck, engines make up 58 percent, making them the largest contributors in total fuel consumption. When evaluating a truck engine’s efficiency, here are three things to consider:

Engine Components
Due to the amount of energy lost in the combustion process, a typical diesel engine is 40-50 percent efficient in converting diesel to propel a truck forward. Getting the most out of the engine’s efficiency requires running it at the right revolutions per minute (RPM). 

Many modern engines, including the PACCAR MX and Cummins ISX15, were designed with fuel economy in mind. Over the last few years, advancements in the below technologies have been designed and incorporated in engines to optimize fuel economy:

- Reduced internal drag    - Cylinder head design   - 2,500 bar common rail fuel system
- Aftertreatment performance   - Injector atomization   - Temperature
- Variable geometry turbo charger   - DEF consumption   - Reduced engine RPM
- Piston design   - Waste heat recovery   - Accessories

One of the biggest opportunities for engine efficiency within the customer’s control is downspeeding. By lowering the number of engine revolutions at highway cruising speed, there are fewer individual combustion events per mile, and each one consumes less fuel. Current experience indicates that for every 100 RPM drop in engine speed, a 1 percent fuel savings can be seen at highway cruising speeds. 

Electronic controls, variable turbochargers and fuel system changes have led to a broader and more usable torque curve that reduces the need to downshift. Driver training is crucial for individuals used to driving in a different RPM range.


Industry changes in transmission and axle oil have given customers improved fuel economy. Hubs and outer ends have adopted new lubrication to improve friction and rolling resistance.

Temperature of oil affects fuel economy losses. Liquids tend to get thinner or less viscous as they are heated, which allows oil to move more easily around the vehicle’s moving parts. To achieve a 1 percent fuel economy benefit, 10w-30 became the standard factory fill on the MX engine, over 15w-40. Consult an engine manual to review which lubricant is the best for the vehicle’s mechanical components based on geography.

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