Same Pump. Different Fuel.
In Europe, CP4 failures are reported at well under 1%, thanks to stricter lubricity standards.
Failure rates in the U.S. have been documented as high as 7% — that’s about 1 in 14 trucks.
DIESEL FROM THE PUMP IS HARMING YOUR ENGINE
2 min read
Today’s Ultra-Low Sulfur Diesel (ULSD) has far less lubricity than traditional diesel. The refining process that removes sulfur also strips away natural lubricating compounds, leaving the fuel “drier”, increasing metal-to-metal contact and accelerating wear in critical engine components.
This increases the risk of premature failure in critical components such as injectors and high-pressure fuel pumps – most notably the widely used Bosch CP4 has become well-documented for this issue.
Why U.S. Fuel Standards Fall Short
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Lubricity is measured by wear scar diameter (smaller is better)
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U.S. legal limit: up to 520 µm
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Manufacturer recommendation: 460 µm or below
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Typical diesel from the pump is closer to 500 µm, which increases risk of premature failure
Even fuel that meets legal U.S. standards can be unsafe for your fuel pump
Why The CP4 Fails
and the catastrophic impact it can have on your entire fuel system
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Designed for ~460 µm fuel, but often exposed to ~500 µm fuel (or worse)
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The steel cam and pistons grind, rapidly accelerating wear, sending metal shavings through entire fuel system
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Fuel filters become overwhelmed and unable to stop the spread of debris – this is commonly referred to as the CP4 "grenading"
When the CP4 fails, the whole system goes with it
Pump, injectors, rails, filters, and tank all need replaced. Repairs often reach $8,000–$10,000.
CP4 Pumps Fail More in the U.S.
The Bosch CP4 pump isn’t inherently doomed to fail. In fact, it operates far more reliably in Europe. The difference comes down to the fuel
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European diesel has stricter lubricity standards, with wear scar limits set to 460 µm, matching Bosch’s design specification
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In the U.S., ULSD is legally allowed up to 520 µm. This creates a dangerous lubricity gap that pushes the CP4 outside its safe operating range
Same Pump. Different Fuel.
In Europe, CP4 failures are reported at well under 1%, thanks to stricter lubricity standards.
Failure rates in the U.S. have been documented as high as 7% — that’s about 1 in 14 trucks.
The Simple Fix
Archoil AR6500 Diesel Treatment
The simplest way to eliminate the risk of low-lubricity diesel is to treat your fuel at every fill-up with a proven additive that restores the protection ULSD is missing. For high-pressure systems like the CP4, lubricity isn’t optional — it’s essential. Archoil AR6500 Diesel Treatment delivers industry-leading protection where it matters most.
In independent testing
AR6500 Reduced Wear By 43%
Wear Scar Before
Base fuel: 614.5 microns (µm)
Wear Scar After
Fuel with AR6500: 347.5 µm
What is the test for lubricity?
ASTM D6079 – High Frequency Reciprocating Rig (HFRR) Test
The HFRR test measures lubricity by oscillating a metal ball against a metal plate while immersed in fuel. Afterwards, the size of the wear scar on the ball is measured — the smaller the scar, the better the fuel protects against wear.
AR6500 reduced the wear scar of low quality diesel from 614.5 µm all the way down to just 347.5 µm. That's not just compliant, but well below even the strictest manufacturer recommendations – providing far greater protection for your fuel pump and injectors than what standard ULSD alone can offer.
The Only Additive Your Diesel Needs
AR6500 is a complete diesel treatment. In addition to outstanding wear protection, it improves fuel quality across the board:
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Boost cetane up to 8 points for smoother combustion, faster cold starts, and better fuel economy
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Clean injectors and maintain a clean fuel system and post-combustion system (turbo and DPF) with advanced detergents
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Improve diesel fuel economy 6-10%+
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Fewer regens, less soot and smoke, and a quieter, more efficient engine
Treat your diesel every tank and you’ll protect your fuel system from wear, extend the life of critical components, and gain noticeable improvements in performance, fuel economy and reliability.
