Best Diesel Fuel Additives: Cetane Boosters & Lubricity
Why Additives Matter on Modern Diesels
US diesel fuel after the 2006 Ultra Low Sulfur Diesel mandate has roughly 1/500th the sulfur of pre-2006 fuel. Sulfur was a major contributor to lubricity -- the film strength that lets metal parts slide against each other without galling. ASTM D975 specifies a maximum HFRR wear scar of 520 microns, but Europe specifies 460 and many OEM manufacturers recommend 460 or lower for their high-pressure fuel systems. US pump diesel often tests at 500-540, right at the edge. This matters most on high-pressure common-rail systems running Bosch CP4 pumps (2011-2019 6.7 Power Stroke, 2011-2016 LML Duramax) where the cam-and-tappet interface has no separate lubrication -- the fuel is the lubricant. Cetane number on US pump diesel averages 42-44; most diesel engines are happier at 47-50.
Lubricity Additives Worth Running
Hot Shot's Secret Diesel Extreme and Stanadyne Performance Formula are the benchmark lubricity additives in the US market. Both drop HFRR wear scar numbers by 80-120 microns (into the European range) when used at label dose. Archoil AR6200 Ultimate Diesel Fuel Treatment is a newer entrant with similar lubricity performance plus claimed injector cleaning additives. Treat rate is typically 1 ounce per 5 gallons or 1 bottle per 30-gallon tank. Running a lubricity additive every tank on a CP4-equipped truck is cheap insurance -- $5-$8 per tank against a $7,000-$12,000 fuel system replacement if the pump grenades. Skip no-name lubricity additives that do not publish HFRR test data; several cheap products on Amazon actually raise wear scar numbers because they are primarily solvent with no real lubricity package.
Cetane Boosters: When They Help
Cetane boosters use 2-ethylhexyl nitrate (2-EHN) to improve ignition quality. Higher cetane means the fuel starts burning sooner after injection, which shortens the ignition delay, reduces peak pressure spikes, and generally produces smoother running and slightly better cold-start behavior. Power Service Diesel Kleen (the gray bottle) bumps cetane by 3-6 points depending on starting fuel quality. Stanadyne Performance Formula adds about 5 cetane. Lucas Oil Diesel Deep Clean includes a cetane boost component. Cetane boosters pay off most on older mechanical injection diesels (7.3L Power Stroke, 12-valve Cummins, mechanical Duramax), where low cetane pump fuel causes hard starts and rough idle. On modern common-rail trucks, cetane boost is a modest improvement rather than a must-have -- the ECM compensates for low cetane by adjusting timing.
Winter Anti-Gel: Non-Negotiable in Cold Climates
Diesel fuel contains paraffin wax that starts to crystallize around 20 degrees F and solidifies into gel by -10 F without treatment. A gelled tank will not flow through the fuel filter and the truck will not start. Winter blends sold at northern US pumps include anti-gel but the protection level varies by station and is never as strong as aftermarket treatment. Power Service Diesel 911 is the rescue product when fuel has already gelled -- pour it in the tank and fuel filter, wait an hour, and it re-liquefies the wax. Power Service Diesel Fuel Supplement (the white bottle) is the preventive product; treat every tank from November through March if you are in the northern US or Canada. Hot Shot's Secret EDT has a strong cold-weather package too. The cost is about $8-$12 per tank treatment -- failing to treat can leave you stranded in a parking lot at 3 AM waiting for a tow.
Product Picks for Common Use Cases
CP4-equipped 6.7 Power Stroke or LML Duramax: Hot Shot's Secret Diesel Extreme every tank (lubricity + cetane + injector clean). Cold-weather commercial truck: Power Service Diesel Fuel Supplement from November through March plus a bottle of Diesel 911 in the cab for emergencies. 5.9L or 6.7L Cummins commuter: Stanadyne Performance Formula every tank. Older 7.3L Power Stroke or 12-valve Cummins: Stanadyne or Lucas Upper Cylinder Lubricant as a lubricity baseline plus an occasional full-strength injector cleaner like BG 44K or Hot Shot's Everyday Diesel Treatment. Avoid gimmicky 'enzyme' or 'ceramic' additives from lesser-known brands -- most of the magic marketing claims do not show up in lab testing.
What Additives Will Not Fix
Additives are preventive and maintenance tools, not repair products. They will not clear a clogged DPF, fix a failing CP4 pump, repair a cracked injector, or resurrect a dead SCR catalyst. Running heavy doses of injector cleaner through a truck with existing damage can actually loosen debris that goes on to plug the fuel filter or injector tips. If a truck has active fault codes for fuel pressure, injector performance, or emissions efficiency, get it diagnosed first and use additives as follow-up maintenance, not as a magic bullet. Finally, some additives are not legal for on-road use in California -- check the label for CARB compliance before buying if you register in a strict state.
Recommended: Hot Shot's Secret Diesel Extreme
The most recommended lubricity additive for CP4-equipped trucks (6.7 Power Stroke, LML Duramax). Drops HFRR wear scar by 80-120 microns, includes cetane boost and injector cleaning. One bottle treats 80 gallons. At about $15-18 per bottle, that is roughly 1 cent per mile of CP4 insurance against a $7,000-$12,000 fuel system failure.
- Best-in-class lubricity improvement for CP4 pump protection
- Cetane boost + injector cleaning in one product
- 1 bottle treats 80 gallons
- ULSD and DPF safe
- Premium price vs basic cetane-only products
- Not a rescue product for already-gelled fuel
- Does not replace winter anti-gel in cold climates
Verdict: The go-to additive for any CP4-equipped diesel. Run it every tank -- at $0.01/mile it is the cheapest insurance on your truck.
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Cold Weather Essential: Power Service Diesel Fuel Supplement
The white bottle. Non-negotiable from November through March in the northern US and Canada. Prevents wax crystal formation that gels fuel lines and starves the engine. Keep a bottle of the companion product Diesel 911 (the red bottle) in the cab for emergencies -- it re-liquefies already-gelled fuel in about an hour.
- Prevents fuel gelling down to -40F at full treat rate
- Includes cetane boost component
- Available at every truck stop and parts store
- Also protects fuel filter from wax plugging
- Must be added before fuel gels -- not a rescue product
- Treat rate varies by temperature, read the label
- No significant lubricity benefit vs Hot Shot's
Verdict: Every diesel in a cold climate needs this from November through March. A $12 bottle vs a $300 tow bill and a missed day of work.
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Frequently Asked Questions
Should I run additives every tank or just some tanks?
On a CP4-equipped truck in the US (2011+ 6.7 Power Stroke, 2011-2016 LML Duramax), run lubricity additive every tank without exception. On older or more robust fuel systems (5.9 Cummins, 7.3 Power Stroke, LBZ Duramax), every other tank or even once a month is reasonable. Cetane boost is most useful in cold weather and for towing heavy loads; off-season it is optional. Winter anti-gel is every tank from November to March in the cold belt.
Will additives void my powertrain warranty?
EPA-certified on-road diesel additives from established brands (Hot Shot's, Stanadyne, Power Service, Archoil, Lucas) do not void warranty when used at label dose. The Magnuson-Moss Warranty Act protects consumers from warranty denial over aftermarket fluids unless the manufacturer can prove the additive caused the specific failure. In practice, dealers rarely challenge additive use. Avoid untested no-name products for this reason too -- if a failure is traced to a weird additive, the warranty fight gets expensive.
Are there any additives Ford specifically recommends for CP4 protection?
Ford's official position has been that using additional fuel additives is not required. Independent testing by Diesel Tech Magazine and others has repeatedly shown that lubricity additives do reduce CP4 wear, but Ford will not officially endorse any product for liability reasons. The recommendation to run Hot Shot's or Stanadyne comes from the diesel community, not from Ford. Ford did extend CP4 warranty coverage on some trucks via internal service actions but never publicly recommended additives.
Can additives damage the DPF or emissions system?
Quality on-road diesel additives are formulated to be DPF-safe. Avoid products that contain metallic components (tin, iron, copper) -- some older additives used metal-based combustion catalysts that contaminate DPFs and SCR catalysts. Any product sold as 'ULSD compatible' or 'low-SAPS' (low sulfated ash, phosphorus, sulfur) is safe for modern emissions hardware. If the label does not specifically call out ULSD/DPF compatibility, skip it.
How much do fuel additives actually cost per mile?
A bottle of Hot Shot's Diesel Extreme treats 80 gallons of fuel and costs about $15-$18. At 20 MPG, 80 gallons is 1,600 miles, so the cost is about 1 cent per mile. Winter anti-gel is similar. That is cheaper than the increase in fuel economy many additives deliver (0.3-0.8 MPG improvement in controlled testing) and trivially cheap compared to the cost of CP4 failure or a winter gelling incident.