BD Diesel Automatic Transmission Oil Cooler Bypass Tube Eliminator

Why the OEM Cooler Bypass Tube Is a Known Weak Point

Owners of Ford 7.3L Power Stroke-powered Super Duty trucks running the 4R100 automatic transmission — and Dodge RAM diesels equipped with the 68RFE or Aisin AS69RC — share a common vulnerability baked right into the factory design: the OEM transmission oil cooler bypass tube assembly. Automatic Transmission Oil Cooler Bypass Tube Eliminators exist because this factory valve has a well-documented history of failing or sticking, routing hot fluid back through the transmission instead of through the external cooler — precisely when thermal management matters most, like during hard acceleration or heavy towing.

The factory bypass valve was designed to divert fluid away from the cooler during cold starts so the transmission warms up faster. The problem is that debris, wear, and corrosion can cause it to jam in the open (recirculation) position. When this happens, the transmission temperature will rise and the cooler you paid for does nothing. The result is accelerated clutch pack wear, shortened transmission life, and — in severe cases — catastrophic failure on the road.

BD Diesel's Solution: Permanent Bypass Deletion

BD Diesel has been engineering solutions for diesel powertrains since the early 1970s, and their approach to this problem is characteristically straightforward and durable. The BD Diesel Automatic Transmission Oil Cooler Bypass Tube Eliminator kit (part #1600036 for the 1999–2003 Ford 4R100) permanently removes the problematic OEM cooler bypass tube assembly and replaces it with precision-machined aluminum shunts and sealing washers. This ensures 100% of the transmission fluid flows through the cooler at all times, keeping operating temperatures as low as possible under any load condition.

The kit is designed as a straightforward preventative maintenance item. It's especially well-suited to installation during a transmission service, when fitting an aftermarket cooler, or when rebuilding the unit entirely. BD Diesel also includes this bypass eliminator as a standard component bundled with all of their 4R100 transmission kits, Auxiliary Filter kits, Xtruded Cooler kits, and Built-It rebuild kits — a sign that BD considers it a non-negotiable upgrade rather than an optional add-on.

Who Needs This Kit?

• Heavy towers: Trucks that regularly haul trailers, campers, or heavy loads generate significantly more transmission heat. Guaranteed full-flow cooling is essential.
• High-mileage Super Duty owners: Aging bypass tubes are prone to corrosion and failure to fully seat, quietly robbing you of cooling efficiency.
• Rebuilders and installers: If you're already inside the transmission or installing an aftermarket cooler, eliminating the bypass valve is a logical, cost-effective step that protects the entire investment.
• Mountain and grade drivers: Extended descents and climbs place sustained thermal demands on the transmission that the OEM bypass system is not equipped to manage reliably.

BD Diesel's Transmission Expertise

BD Diesel's credibility in the bypass eliminator category stems from their broader mastery of diesel transmission engineering. The brand specializes in Ford, Dodge, and GM/Allison truck transmissions, offering application-specific valve bodies, accumulator bodies, and some of the most robust torque converters in the aftermarket. Their in-house design and manufacturing process means every component — down to the aluminum shunts in this kit — is held to the same standard as their fully built transmission assemblies. This bypass eliminator kit is legal for sale and use in all 50 states and requires no emissions exemption order in California.