Bringing Euro-Spec Cooling to All Mkiv Supras - The Billet Rear Oil Cooler Adapter

The Supra’s Hidden Cooling Feature

The Mkiv Toyota Supra is known for its legendary performance, but one of its rarest features is something most enthusiasts have never experienced: the Differential Oil Cooler found only on Euro-Spec Supras.

This factory system has a bespoke differential assembly with an external oil pump and utilized the RH rear quarter vent to help regulate differential temperatures. However, it was never offered globally—leaving most Supra owners without this unique cooling advantage.

While Toyota has not officially stated the exact reason for including this feature, enthusiasts speculated that it was designed with sustained high-speed driving on the German Autobahn in mind.

That’s where our Billet Rear Oil Cooler Adapter System comes in.

How it Stands out from Traditional Custom Solutions

For years, enthusiasts looking to replicate this feature had to rely on custom fabrication. Some owners went as far as welding plates onto aftermarket oil coolers, but these solutions had downsides:

• Lack of precision – Hand-fabricated mounts don’t always maintain ideal airflow.
• Structural concerns – Welding directly onto an oil cooler can compromise its integrity.
• Limited versatility – A welded setup is often a one-off solution, preventing the ease of long-term serviceability.

Rather than relying on custom work, we wanted a consistent CNC-machined solution that integrates seamlessly with the Supra’s rear quarter vents - without the need for cutting or welding.

 

The Journey Behind the Billet Rear Oil Cooler Adapter

Creating an OEM+ solution that seamlessly integrates with the Supra’s rear quarter vent wasn’t an overnight process—it took extensive design, testing, and refinement to ensure the perfect fit.

A Project Nearly a Year in the Making

This project began in June of (2024), with the goal of developing a true bolt-on rear-mounted oil cooler solution that didn’t require welding or excessive fabrication. Over the course of development, the design evolved through 550+ different iterations in Fusion 360, refining every small detail - including tolerances, p-clamp locations, radius matching, ducting transition shape, threads, tying the pillars together, running it through simulations, etc. With each iteration, new refinements emerged, and the design continued to evolve.

Throughout the process, we experimented with multiple 3D solid models, pushing the boundaries by testing larger oil coolers while maintaining clearance for the rear tires. To validate the design, we 3D-printed multiple test models and conducted real-world test fittings on the car, ensuring that everything aligned as intended before committing to full CNC production.

A Solution for Limited Front-Mount Options

Beyond its connection to Euro-Spec Supras, this project was driven by another realization: not every Supra owner can fully duct their front bumper holes due to space limitations from front-mount intercooler piping. This inspired us to provide an alternative cooling solution, giving owners more flexibility to optimize their cooling strategy without compromise.

A Last-Minute Challenge That Made It Better

As development neared completion, my friend Tuan (a.k.a Suprabiologist on Supraforums) challenged me to integrate an oil line shield into the design. While I had originally considered this feature, I wasn’t sure how to execute it effectively and was close to setting it aside. His input pushed me to refine the concept, leading to a valuable last-minute improvement that ensures better protection for the oil lines and longevity.

The Engineering Behind the Billet Rear Oil Cooler Adapter

Our goal was simple: create an OEM+ bolt-on solution that maximizes cooling efficiency while maintaining a factory-like fit and finish. But to achieve that, we had to solve several challenges:

Finding the Right Oil Cooler

To ensure maximum cooling performance, we conducted extensive research on aftermarket oil coolers to find the largest possible unit that:

• Fits within the rear quarter vent while maximizing tire diameter clearance.
• Maintains smooth airflow transition to optimize cooling efficiency.
• Allows proper serviceability - oversizing the cooler could disrupt the carefully designed transition shape of the duct serviceability, affecting both fitment and overall integration.

After evaluating multiple options, we have ultimately selected Setrab, a brand with an extensive OEM background in high-performance vehicles like the Lexus LFA and Ferrari F40.

Their recently released ProLine SLM (Slim Line) oil coolers are over 20% slimmer than their standard ProLine models, providing additional tire diameter clearance.

Additionally, the SLM series turned out to be a perfect match for the Supra’s quarter vent opening, striking an ideal balance between cooling efficiency, compact size, and seamless integration. Its dimensions align exceptionally well with this application.

The cooler we have ultimately decided on was:
Setrab PN: 53-10741-01
Description: SLM141-10

 

Eliminating the Need for a Gasket

We paid close attention to the radius dimensions of the Setrab core, matching them as precisely as possible to create a seamless interface. This level of precision eliminates the need for a gasket.

Vibration Control: Toyota Already Did the Hard Work

One of the key considerations when mounting an oil cooler is vibration control, as excessive vibrations can lead to premature stress, cracks, and ultimately failure.

Fortunately, Toyota had already addressed this in the factory design. The rubber duct that overlays the mounting holes on the chassis not only seals, but also serves as a vibration damper, effectively reducing unwanted resonance. Because of this, we were able to hard-mount the oil cooler onto the CNC-machined duct without introducing excessive vibrations or stress to the system.

This ensures a durable, secure fit while maintaining smooth airflow and cooling efficiency. We want to extend our appreciation to Toyota and their Engineering Team for considering this in their design, allowing us to develop a solution that integrates seamlessly with their vision.

A 5-Piece Modular System for Maximum Durability

Unlike single-piece adapters, our Billet Rear Oil Cooler Adapter System is a 5-component kit, each designed for a specific function:

1. Billet Oil Cooler Adapter (LH & RH options) – Provides a precision-machined mounting solution for both sides of the vehicle.
2. Aluminum Mesh Shield – Protects the oil cooler from debris while maintaining airflow.
3. P-Clamp (2) & Oil Line Shield – Replaces the factory plastic shield with CNC-machined aluminum for maximum durability.

This isn’t just a mounting bracket - it’s a complete OEM+ cooling integration that ensures performance, protection, and longevity.

Why This Is an OEM+ Solution for Supra Owners

 

• Direct Bolt-On – Precision machined for a factory-like fit.
• LH & RH Variants – Unlike the factory Euro-Spec unit, we offer both, a left-hand and right-hand version, so owners can utilize both vents.
• Versatile Applications – While originally designed for an oil cooler, this adapter can be used for other powertrain components such as:

1. Transmission coolers
2. Auxiliary radiators
3. Power Steering
4. Other systems with a Standalone Pump

Who This is For

Whether you’re a track enthusiast, high-horsepower builder, or someone who appreciates rare factory-inspired upgrades, our Billet Rear Oil Cooler Adapter lets you unlock a rare Euro-Spec advantage - with a precision-machined, direct-fit mounting solution.

Bring factory-inspired cooling performance to your Supra today. Upgrade now!