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How to Save Big Money on Diesel Exhaust Fluid (DEF) and Engine Maintenance.

Updated: Jul 17

Long-haul trucker runs cleaner engine and can achieve $11,250 in annual savings, per truck, with new combustion system.


Diesel Exhaust Fluid (DEF) is a urea and water solution that is sprayed into the exhaust stream of diesel engines to break down dangerous NOx emissions into harmless nitrogen and water. This system is called Selective Catalytic Reduction (SCR) and can be found on 2010 and later model year trucks.


Over the past several years, SPI.Systems Corporation has conducted extensive research and road testing to determine whether enhanced combustion requires less DEF, which leads to reduced contamination from Exhaust Gas Recirculation (EGR) and cleaner diesel engine operation.


We are pleased to report that the answer is yes, and we now have road-proven results to confirm the cost savings.


Experiments with a new system of combustion enhancement known as SPIER on 15-liter engines show that, on average, SPIER reduces the percentage an EGR valve is open from 43% down to 27%. Consequently, the amount of DEF usage, with the vehicle pulling the same loads over similar routes and speeds equipped with SPIER, was down by 30%. That correlation repeats enough that lower DEF usage is now a trusted predicter of reduced EGR activation, fewer EGR system failures, reduced soot loading, less engine oil contamination, and reduced turbo seizures, plus lower expenditures for DEF.


So, what do we save in DEF? One SPIER user, a long-haul trucker who regularly runs his Class 8 from Pennsylvania to California, used to get 110.7 miles/gal of DEF. Now he gets 144.1 miles/gal, for a reduction of 30%. Round trip usage of DEF was 38 gallons instead of 54. So, at an average cost at the pump of $3.00/gallon, he saved $48 in one week just in DEF. At a store he might pay 3X that price. At 50 weeks he would save $2,400 per year per truck. But that’s only part of the benefit of reduced EGR. By running a cleaner engine, our trucker reduced the need for maintenance of his engine in a major way. Let’s see why by looking at the impact of soot spread into the diesel engine by the EGR system, along with less need for SCR injections of DEF.




We can think of the EGR system as a major source of soot contamination throughout its own piping and back into the engine cylinders and oil. What’s that cost?


Here’s a list of typical maintenance cost reduction reported by a 400-truck long-haul fleet by using SPIER to cut soot loading from EGR: Maintenance and Unplanned Downtime


SPIER reduces costly contamination of the emission control system and the associated aftertreatments, reduces the load upon the EGR and SCR systems due to lower NOx levels, cuts oil contamination and cylinder wear, and cuts fault codes caused by faulty sensors and turbocharger failures.

The following are records from both city and highway vehicles.


Factors of improvement with SPIER for 400 trucks:

FAULT CODE COSTS REDUCTION/TRUCK/DAY = $2/Day X 400 = $800/day x 240 day/yr. = $192,000/yr.

EGR Maintenance Reduction = 25% x 400 x $5000/yr./truck = $500,000/yr.

PM FILTER CLEANING REDUCED 5 DAYS/MO X$300/CLEANING = $4/DAY X 240 days x $400 = $384,000/yr.

ENGINE REBUILD REDUCED 25% = $6800/Yr./truck x 400 = $2,727,000 /yr.

DEF Usage and SCR Catalyst Replacement Reduction Estimate 25% x 400 x $2000/yr./truck =$200,000

Turbocharger Failure Reduction from Cleaner Oil Estimate = 25% reduction x400 x $5000 =$500,000/yr.

Total = 44,503,000/yr.


Now, the true total benefit of SPIER’s reducing EGR activity becomes clear: $11,258/truck.


We are seeing consistent results in all climates and temperatures, which is great news for the owner/operator and for fleet owners that are always looking for new ways to cut costs and deliver loads as efficiently and environmentally responsibly as possible.


To learn more about decreasing DEF and engine maintenance while improving overall diesel fuel consumption, click here.


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