FLEECE FPE-CLNTBYPS-CUMMINS-0305 CUMMINS COOLANT BYPASS KIT 2003-2005 AUTO TRANS

Cure rear-cylinder hot spots on your 2003–2005 5.9L Cummins (automatic) with the FLEECE FPE-CLNTBYPS-CUMMINS-0305. This proven bypass adds a temperature-based secondary thermostat to stabilize coolant flow at the back of the block—reducing pressure spikes, protecting freeze plugs, and improving towing consistency and longevity. Fleece coolant bypass 03-05 automatic, 5.9 Cummins rear cylinder cooling, freeze plug protection, CPP Diesel Fleece Performance, temperature-based secondary thermostat, plug and play kit

Why this Fleece kit

• Temperature-controlled secondary thermostat evens out coolant temps across all six cylinders
• Helps prevent rear freeze-plug failures and coolant over-pressure
• Complete, leak-resistant install with braided hose and AN O-ring fittings
• Billet hose brackets included for MY2003+

Fitment

Engine: 2003–2005 Ram 2500/3500 with 5.9L Cummins (24-valve common rail)
Transmission: Automatic (replaces/omits OE heat exchanger per kit design)
Notes: Designed to stabilize rear-cylinder temperatures and reduce cooling-system pressure.

Cross-Reference / Related Fleece Items (CPP Diesel)

• FPE-CLNTBYPS-CUMMINS-0305-SS — 2003–2005 Auto (Stainless Line)
• FPE-CLNTBYPS-CUMMINS-0607 — 2006–2007 Auto
• FPE-CLNTBYPS-CUMMINS-MAN — 2003–2007 Manual
• FPE-CLNTBYPS-HS-HC-0305 — Replacement Hose (2003–2005)
• FPE-CLNT-HS-BRKT — Coolant Bypass Brackets (2003–2007)
• FPE-CUMM-HCL-0324 — Heater Core Replacement Hose & Fitting

Uneven coolant distribution makes the rear cylinders run hotter, driving pressure spikes that can pop freeze plugs. The Fleece bypass evens temperatures and relieves pressure before it becomes a failure.

No tuning required. The kit is engineered as a bolt-on with model-specific plumbing and brackets.

On 2003–2007 5.9L automatic models, the kit eliminates the OE heat exchanger. It is not a cooler and isn’t required in warm climates or higher-power applications.

Yes—see the stainless-braided variant linked above for the same fitment with upgraded hose construction.

Specifications for FLEECE FPE-CLNTBYPS-CUMMINS-0305