Since 1995, U.S. Environmental Protection Agency (EPA) emission rules have mandated that off-road engine manufacturers gradually phase in lower emitting diesel engines across all tractor and other off-road equipment sold in the United States. Starting in 1996 with Tier 1 emission standards for tractors between 175-750 horsepower (hp), all tractors were scheduled to be rated as Tier 4 Final by 2015. During the transition period, emission credit agreements made between manufacturers and EPA allowed for nonattainment of some tractors such that several tractor models were produced post 2015 that did not meet Tier 4 Final standards. Tier 4 standards are primarily concerned with reducing nitrous oxide (NOx) and particulate matter (PM) pollutants, requiring a 90% emission reduction of both compared to Tier 3 standards. NOx contributes to formation of ground-level ozone, while particulate matter is implicated in respiratory illnesses.

With the new emission standards, manufacturers were required to implement emission reduction technologies. Emission reduction technologies such as diesel oxidation catalysts (DOC), diesel particulate filters (DPF), and/or selective catalyst reduction (SCR) systems on the exhaust were developed to break down NOx, resulting in cleaner burning engines. It is important to note that the emission targets do not dictate how manufacturers meet the standards. As a result, a wide array of emission reduction strategies were developed by manufacturers that affect engine fluids use, costs of ownership, and typical maintenance costs3. As tractor emission systems advanced through the stricter emission standards, anecdotal evidence from growers suggested a decrease in fuel efficiency.

Two primary questions drive this research: First, can Tier 4 tractors claim greater emission reductions via fuel efficiency? Second, do Tier 4 tractors have a higher cost of ownership via normal maintenance and repair?

To assess the change in fuel efficiency over time, we estimated the rate of change of fuel efficiency through Tier 4 Final emission standards and provide estimates for factors that have impacted fuel efficiencies using University of Nebraska Tractor Test Lab (NTTL) data from 1988 to 2021. To assess the costs of Tier 4 tractor ownership, we developed a grower survey sent to San Joaquin Valley producers. We asked specifically about the costs of ownership through repair and maintenance costs at various EPA emission tiers and horsepower. We also interviewed equipment repair businesses throughout the San Joaquin Valley to gain their perspectives on costs of repairs and maintenance and to assess whether any issues arose with Tier 4 equipment.

One important deliverable for the project was the development of a searchable database for hundreds of NTTL reports. The NTTL is the only third-party tractor test laboratory in North America, and all manufacturers who want access to the Nebraska and thus the U.S. tractor market must send their tractors there for testing. A partial database of NTTL reports can be found at https://tractortestlab.unl.edu.

The final project report is organized into two sections: the first reports on tractor fuel efficiencies and the second deals with differences in Tier 4 tractor repair and maintenance costs. The notable findings from each report are reported as follows:

Fuel Efficiency vs Emissions

  • Tier 4 Final tractors are statistically more fuel efficient on average than earlier Tiers.
  • The average percent change in fuel efficiency, measured as hp.hr/gal, in Tier 4 Final tractors has been 0.77% per year since 2015. This is compared to an average percent change in fuel efficiency of 0.55% per year across all tractors from 1987-2021.
  • AGCO/Massey has produced the most fuel-efficient tractor, the AGCO Fendt/Challenger 1042 with a hp.hr/gal of 21.17, and John Deere has the highest average fuel efficiency throughout its tested tractors over the same period, 2001 to 2021.
  • Fuel efficiency is consistently lower when tractors are not running at max power.
  • We found statistically significant differences of average fuel efficiency at max power between tractor attributes for Time, Max power take-off (PTO) horsepower, and the interactions between Manufacturer, Chassis, and EPA Tier.

Tier 4 ownership and Maintenance Costs

Farm Survey

  • Growers reported a wide variation in repair and maintenance hours across tractor emission tiers and horsepower.
  • Growers reported paying an average of $20.39/hr for on-farm tractor repair by farm employees vs an average of $123.33/hr and $129.29/hr for independent mobile and in-shop repair services.
  • The majority of respondents (likely those with newer tractors) had equipment still under warranty.
  • Tractor manufacturer suggested retail prices (MSRP) are not available, nor are standard lease rates; industry contacts confirmed that dealers keep that information confidential.

Service Provider Interviews

  • All service managers reported both shop and mobile services.
  • The average reported shop rate was $135/hr.
  • The average reported field rate was $150/hr.
  • Most service managers reported several thousand dollars of investment in computers/tablets/cell phones/hotspots and software per technician.
  • Operator error is one of the most common reasons for emissions-related service calls. All service managers noted the need for more owner/operator education on emission system operation and maintenance.
  • Common operator mistakes include:
      1. Some operators will make simple but very expensive mistakes like putting diesel exhaust fluid (DEF) into a fuel tank;
      2. Running tractors at low RPMs results in de-rating or re-gen modes, which require an expensive service call (minimum $200 -$300 to reset the system); and
      3. Failing to refill the DEF tank.
  • On average, service managers reported 30-35% of their calls were related to emissions systems.
  • Most service managers noted that newer Tier 4 tractors are still under the manufacturer’s emission warranties, so owners are not yet experiencing out of pocket costs for maintaining the emission systems.



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URL: https://digitalcommons.calpoly.edu/agb_fac/161