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Call or Text (352) 722-5295Fuel and DEF tanks on the 2019-2024 RAM 6.7L Cummins
The fuel tank on a crew cab short-bed truck holds 31 gallons, and other cab and bed combinations vary. Inside it, an electric lift pump feeds the frame-mounted water separator, the engine filter and the high-pressure pump. The DEF tank is just as busy: it houses the Bosch Denoxtronic module, with the DEF pump, heater and level-quality sensor, that supplies the selective catalytic reduction system on every 2019-2024 Cummins pickup. The engine is approved for ULSD and biodiesel blends up to B20; going past that limit risks fuel-system corrosion.
What goes wrong at the fill
Two things on this generation touch the tanks. The first is mis-fueling. On one 2020 Ram 3500, a dealer traced a check-engine light and DEF warning to diesel fuel contaminating the DEF. That's an owner report rather than a pattern, but it shows how real the risk is. The second is the CP4.2 on 2019-2020 trucks. When one fails it sheds metal into the rail, injectors, lines and the fuel tank itself. Recall 21V-880 (Y78) replaced the CP4 with a CP3, reflashed the PCM and inspected the fuel system, and some owners still report misfires afterward, with contamination left in the system the usual suspect.
Stock replacement vs. upgrade
A billet cap is a straight swap on the factory filler, with no change to how either system works. Bigger changes involve the tank itself. If you're weighing a high-capacity replacement fuel tank, the 52-gallon crew cab short-bed and 56-gallon crew cab long-bed designs on the market reuse the OEM sending unit and pump seal, and the gauge on those tanks reads full for the first 8-10 gallons. Whatever tank you run, a lubricity additive at every fill, compatible with the DPF and SCR, is the standard preventive step on CP4 trucks and harmless on a CP3.
What we carry
Right now this collection holds billet fill caps from Pacific Performance Engineering (PPE):
- PPE 273003000 billet fuel cap with a built-in magnet, anodized green, listed for 2019-2025 6.7L trucks.
- PPE 273005000 billet DEF cap, anodized blue, with a listed fitment range that covers every year on this page.
Green on the diesel filler and blue on the DEF filler gives you a quick visual check before the nozzle goes in.
Fitment notes
Each cap lists a fitment range wider than this page's years, and the ranges differ between the fuel and DEF caps, so check each listing with the fitment checker. Fuel-tank size depends on cab and bed, with 31 gallons on crew cab short beds, so verify by VIN before you order anything that replaces or modifies the tank. Rebel trucks from 2023 on, where the Cummins was optional, also carry a factory skid plate that protects the fuel tank.
Frequently asked questions
Does the magnetic PPE fuel cap protect a CP4 pump?
Don't count on any filler part for that. On 2019-2020 trucks the factory remedy was the Y78 recall, which replaced the CP4.2 with a CP3; any truck without documented Y78 completion should get it done, free, at the dealer. A DPF- and SCR-compatible lubricity additive at every fill is the standard preventive step.
What fuel can I run in a 2019-2024 6.7L Cummins?
ULSD, and biodiesel blends up to B20. Going past the biodiesel limit risks corrosion in the fuel system. In extreme cold, add an anti-gel on top of the lubricity additive.
What if diesel ends up in the DEF tank, or DEF in the fuel?
Have it diagnosed rather than guessing. On one 2020 Ram 3500, a dealer traced a check-engine light and DEF warning to diesel contaminating the DEF, and fuel-system damage is the other outcome tied to mis-fueling. The DEF tank also houses the Denoxtronic pump, heater and level-quality sensor module.
Will a bigger fuel tank fit my truck?
It depends on cab and bed. Crew cab short beds come with a 31-gallon tank, and replacement tanks are bed-length specific: 52-gallon designs for crew cab short beds and 56-gallon designs for crew cab long beds, both reusing the OEM sending unit and pump seal. Verify your tank by VIN before you order.
Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.