Fleece Performance Engine Coolant Bypass Hose

Why Fleece Performance Coolant Bypass Hoses Matter for Your Cummins

If you own a Ram with a 5.9L or 6.7L Cummins, coolant distribution is one of the most critical — and most overlooked — aspects of long-term engine health. Engine coolant bypass hoses are at the heart of how Fleece Performance addresses one of the Cummins platform's most well-documented weak points: uneven coolant flow to the rear cylinders.

The rear cylinders of the 6.7L Cummins are notorious for receiving inadequate coolant flow, which leads to elevated temperatures and excessive pressure buildup. Left unchecked, this can cause catastrophic results — including blown freeze plugs in the block and head. Fleece Performance's coolant bypass system reroutes coolant flow to solve this problem at its source, and the bypass hose is the backbone of that system.

What Sets Fleece Performance Bypass Hoses Apart

Fleece Performance takes a notably different engineering approach from competing brands. Their bypass system uses a secondary thermostat that operates based on temperature rather than pressure — meaning the system intervenes before dangerous pressure spikes ever develop, ensuring consistent temperatures across all six cylinders. The front coolant bypass thermostat housing also features a built-in AN fitting rather than a coolant spacer block, resulting in a cleaner, more reliable installation with fewer potential leak points.

The hoses themselves reflect that same commitment to quality. Fleece offers replacement coolant bypass hoses in two construction options:

• EPDM hose — A durable rubber compound designed to handle the thermal cycling demands of a working diesel engine, available for 2003–2007 Cummins applications
• Black nylon braided hose — Available for applications including the 12-valve Cummins, offering added abrasion resistance and a clean under-hood appearance
• Stainless steel braided hose — The premium option for 1998.5–2018 Common Rail and VP44 Cummins applications, providing maximum durability and a professional finish

Complete kits include braided hose and AN O-ring fittings engineered for a leak-free seal, and individual replacement hoses are sold separately for owners who already have a Fleece bypass kit installed and need a service part. Fitment spans a wide range of Cummins generations, from the 1989–1998 5.9L 12-valve through the 2019–2024 6.7L 24-valve, making Fleece one of the most comprehensive sources for this application in the diesel aftermarket.

Built and Certified to a Higher Standard

Fleece Performance Engineering, headquartered in Pittsboro, Indiana, holds ISO 9001:2015 Certification — a quality management standard that underscores their commitment to consistent manufacturing processes. The coolant bypass product line is also protected under U.S. patents, reflecting the genuine engineering innovation behind the design. For Cummins owners who want a bypass hose that fits correctly, seals reliably, and addresses the root cause of rear-cylinder heat issues, Fleece Performance is the benchmark in this category.

Browse the full selection of Fleece Performance engine coolant bypass hoses, or explore the complete Fleece Performance catalog for more diesel performance solutions.