What You Need To Know About Differential and Transmission Coolers

While your typical grocery-getter can usually manage internal temperatures without additional cooling beyond a radiator and engine fan, vehicles that see extreme use – like those used in motorsport – need additional coolers that can help maintain the operating temps of the fluids running through not only the engine, but the transmission and differential as well. Our Factory Five Cobra Jet Challenge project build is shaping up to be a serious contender on the road course. With a 5.1-liter Coyote V8 that makes in excess of 625 horsepower, it’s hooked to a Ford Racing six-speed gearbox that sends all that grunt exclusively to the rear wheels through a Moser rear end.

Even though the Cobra is expected to weigh under 2,400 pounds (with a driver), all of that power getting channeled through a pair of massive Toyo tires is going to generate quite a bit of heat out on the road course, and our intention is to build this car not only with performance and safety in mind, but reliability and durability as well. To that end, we’re installing a Derale dual channel cooler and a pair of Tilton fluid pumps, along with Russell hoses and fittings for the plumbing. We will control it all with an AEM Infinity management system.

The drain plug on the rear end has a -6AN feed line with an inline temp sensor that’s wired to the AEM’s Infinity controller. The pump pulls the fluid from the rear end’s drain plug, sends it through the oil cooler (with the fan on the cooler triggered at the same time) then back to the fill plug on the rear end. We used the same design to hook up the transmission as well.

The Cause And Effect Of Operating Temperatures

As temperatures increase, oil viscosity – or its restriction of flow – decreases. This might seem like an inherently positive effect – an oil that’s able to move around the system freely should keep everything well lubricated and protected, right? But it’s not that easy. “Viscosity is a balancing act,” says Lake Speed, Jr. of Driven Racing Oil. “Every 20-degree increase in oil temperature cuts the life of the oil in half, as the oxidation rate doubles.” Oxidation describes the chemical breakdown of the oil as its molecules react with oxygen and its chemical compound starts to change in ways you don’t want it to.

“If the oil is too thick it can’t flow properly – it can’t carry away the heat and lubricate,” says Speed. “But, if it’s too thin, then it can’t cushion the parts which allows contact, and that generates heat and wear.”

The trick is to get the oil to be as close as possible to its optimum viscosity without going under it. So what’s the operating temperature to get to that optimum viscosity? It depends on a number of factors. “A good operating range is generally considered to be around 180-220 degrees, but a manufacturer might expect as much 250-260 degrees in racing context,” Lake explained. Ultimately, it’s important to consult with the parts manufacturers to determine exactly what makes the most sense for your build and what you plan to do with.

Derale's dual channel cooler can support two separate systems with one compact design that can be mounted just about anywhere as long as there's space for it.

What happens when those operating temperatures exceed the oil’s capabilities and oxidation sets in? Premature wear. In transmissions, that means additional strain on internal parts – particularly the synchros in modern gearboxes. “As the oil breaks down, the biproducts that’re caused by that are acidic, and they can cause additional wear and break down seals prematurely,” Speed added.

For differentials, getting the equation right is even more important. “Hypoid rear ends, like the Ford 9-inch, require GL5 hypoid-rated gear oil or you risk destroying the ring and pinion. If sliding contact is allowed between the gears they can “weld” together and immediately separate under high pressure, which causes scuffing, scoring, and a ton of overall wear, so you have to have specialized additives to prevent that,” cautions Speed. “And, not all gear oils do.”

Speed also made an interesting point about the conventional wisdom of having good luck with a particular oil without actually doing the research. “Good luck, to most people, means not having a total failure. That’s pretty far from ideal, and folks often don’t know what they’re missing by using this approach. Seeking out specialized options can often increase the life of parts exponentially.”

Tilton offers these cooler pumps in either intermittent or continuous duty specification. Intermittent use pumps are designed for applications where the cooler pump might be turned on/off by the driver or a relay at established temperatures. Continuous duty pumps are designed for applications where the pumps needs to operate for oever two hours without cool down time.

Tilton offers these cooler pumps in either intermittent or continuous duty specification. Intermittent use pumps are designed for applications where the cooler pump might be turned on/off by the driver or a relay at established temperatures. Continuous duty pumps are designed for applications where the pumps need to operate for more than two hours without cool down time.

Good luck, to most people anyway, means not having a total failure. That’s pretty far from ideal, and folks often don’t know what they’re missing by using this approach. – Lake Speed Jr., Driven Racing Oil

He also pointed out that looking to the industrial field, rather than the automotive/motorsport realm for insight here is far more effective. “The evidence is far more extensive. When you build a ship around an engine – one that’s not ever coming out of the ship – you better believe people are figuring out how to keep that engine alive for as long as possible.” Engineers who work in these fields don’t do time-based maintenance like what’s typical with automobiles – changing your oil every 5,000 miles for exmaple. Instead, they rely on a predictive method which originated in the industrial field and was then applied to racing.

“For serious motorsport use, ditch consumer automotive intervals and adopt industrial considerations.” The cornerstone of this approach is oil and vibration analysis, a technique that samples the oil and analyses it to determine to the health of the oil and the machinery its protecting as well. “It’s the most effective way to safeguard your investment,” Speed added.

Putting Together The Cooling Strategy

If we are sending the differential and transmission fluids through a cooler we’re going to need a way to get them to the coolers and back. For that piece of the equation we’re using two Tilton Racing cooler pumps (PN 40-52X). These pumps feature an internal bypass valve, are self-priming up to 8-feet above the source they draw from and are rated for 50 psi of maximum pressure. They also offer an intermittent maximum temperature rating of 265 degrees F, making them a great choice for the rigors we expect the Cobra to put the system through.

“These pumps flow one to two gallons per minute, depending on the load and fluid viscosity,” adds Kirk Skaufel of Tilton Racing – yet another reason to make sure you get your oil choice right.


Tilton Racing offers its pump with a Buna or Viton rubber diaphragm.  The Buna pump is designed for use with standard oils and coolants, while the  Viton pump is designed for use with corrosive fluids such as gasoline and other fuels.

Additionally, these pumps weigh in at 3.5 pounds each and boast a compact design, which means we aren’t sacrificing much in the way of mass or space.

For the coolers, we reached out to the folks at Derale – they offer a dual channel cooler (essentially two coolers in one unit, stacked on top of each other) that is supplemented with a fan.

We went with the 8 & 8 Pass Dual Circuit Electra-Cool Remote Cooler, -8AN (PN 15200) for our application because its compact design means it can be mounted just about anywhere space permits while supporting two different components, though we reduced the fitting size and lines to -6AN.


Derale’s dual circuit cooler is also available in 4×2 pass and 4×4 pass configurations, and are recommended for use with engine oil, transmission fluid, power steering and fuel systems. When choosing a spot for mounting, keep in mind that the cooler still needs access to airflow to perform at its peak.

The Derale dual channel cooler features a copper/aluminum 8 & 8 pass cooler core and a reversible 10-inch electric fan. With its -8AN x 1/2-inch brass hose barb fittings, the cooler’s design offers a wide range of application possibilities for heat removal requirements.

We had some space on the sides of the fuel cell and choose to mount the Tilton pumps on the left side with the Derale cooler on the right, not only to tuck the components safely away, but also to even out the load a bit.

To hook everything together we turned to Russell Performance for the hoses and fittings. Much like when we utilized their ProClassic II lines for the fuel system, one of the key benefits of Russell hoses is the weight savings over a regular braided line with integrated mutli-wire, as the ProClassic II offers the same strength but does so without the weight of the outer braided material. As we noted while installing that fuel system, incremental weigh savings like this can start to add up, and revisiting them for our transmission and differential cooler lines is a perfect example of how that unfolds.

“The most important recommendations we have for any installation is to make sure the lines are routed with plenty of slack,” notes Eric S. Blakely of Russell Performance and Edelbrock. “This allows for any changes that may occur when the line is under pressure. It’s important to make sure the line or hose is routed with smooth bends and radius to make sure the line is not collapsed or crimped, ensuring that the fluid is flowing at full capacity,” he added.

The ProClassic II hoses are designed to withstand pressures of up to 350 psi and are safe to use with a wide range of fluid types, including oil, antifreeze, and various types of fuel. The full flow ends feature a unique taper design that makes assembly, repair and maintenance quicker and easier. They also offer 37-degree angled sealing surface which guarantees a positive anti-leak seal.

We also wanted a way to control the system and when it would be triggered into action. With the AEM Infinity standalone we can trigger the fluid pumps and the cooler’s fan to turn on at whatever temperature we choose. To get the nitty-gritty on how to configure the Infinity to perform this function, we spoke with Beau Brown at AEM Performance Electronics, who walked us through the layout of the software, and how the various attributes of the system would be configured:


All output setup will be done in the Setup Wizard (under Wizards > Setup Wizard) and then Output Function Assignments which is at the bottom of the Wizard. Select which output you wish to configure, then the type of output you’re setting up. CoolingFan1On is typically the main radiator fan, and is actuated by coolant temperature only.

This can also be set up to turn on as soon as the A/C is activated even if the coolant temp isn’t beyond the trigger threshold. CoolingFan2On setup allows you to use a different temperature input to actuate a secondary fan. This can be a second cooling fan that comes in at a higher temperature (still triggered by coolant temp) or an oil cooler fan, diff cooler fan, etc.

The temperature sensor for the differential runs into one of these inputs and is assigned here. For both of these types of configurations, set an additional condition, which by default is set to RPM. If you set this to 500 rpm, for instance, it will only allow the fans to run when the engine is running to prevent killing the battery. In the example above it is set to 0 rpm.


If you want to do more custom configuration using multiple inputs, set an output to General Purpose and select which inputs you want to use to control it. Then make your adjustments to the corresponding output table under the Outputs tab of the software. When configuring and output in this manner and using a standard automotive relay (i.e. not a PWM controller or solid state relay), make sure to set up the breakpoints so that there is no interpolation between cells.

This must be done with standard relays as you can only send a zero percent or 100 percent signal to them (i.e. fully on or fully off). For instance, an Oiltemp of 111.9 degrees C has a value of 0, and 120.0 degrees C has a value of 100 percent. Same with RPM. This map was configured to turn on LS4 output when oil temp was 120 degrees C and RPM is 500 or higher. You could also use vehicle speed to disable the fan above a certain speed.

Fast-Tracking The FFR Cobra Challenge

With SEMA quickly approaching in November we brought the Cobra into our onsite shop to get the vehicle done in time for the show. There’s just not enough available weekends to get the project built to our satisfaction in time.

The good news is that the Cobra is rapidly coming together and should be road-ready in time to show off to the masses. Be sure to follow updates and progress on the Project Factory Five Cobra Challenge build page.


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About the author

Bradley Iger

Raised by wolves in the far reaches of Orange County, California, Brad is no stranger to the driver's seat, as it is wolf custom to get their offspring up to race pace as early as possible. When not being pulled over in six figure supercars, Brad can often be caught complaining about the DJs in various dive bars around Northeast Los Angeles.
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