MM News

IRS Differential Cooler Tech

The Back Story
When we swapped a 1999 Cobra IRS unit into our 1992 Mustang road race car we installed a temperature sending unit in the bottom of the differential case. The gear oil temperatures we experienced far exceeded Ford's maximum permissible temperature of 230° F. It was obvious that a differential cooler would be required to ensure the longevity of the limited-slip differential.

Before we could begin to design our IRS Differential Oil Cooler, we had yet another test to perform. We wanted to see inside the differential case while the car was at speed, so we would know exactly how the gear oil behaved. This knowledge would ensure that we placed the fittings in the differential case in the best locations. Because the IRS differential cover includes the rear mount, we had to do our testing on a solid axle equipped car. We installed a clear plastic differential cover on the solid axle of a 1990 Mustang. We then lifted that car up and ran it in fourth gear at over 100 mph. The clear differential cover allowed us to see inside the differential case and observe the gear oil while the car was in operation. We saw how the ring gear moved the gear oil around, where the oil ended up, and where the oil was completely absent. Based upon our observations, we placed the pump's suction line in the optimum location to pick up gear oil, and to avoid pulling in air. If the pump sucks in air, the gear oil will become aerated, which will reduce its lubricating ability and the effectiveness of the oil cooling system. At MM we know that proper testing is essential to good design, and our IRS Differential Cooler is a prime example of how invaluable testing is.

Our prototype installation had the oil cooler mounted inside the car, in the spare tire well. For our initial tests we did not duct any air to, or away from, the oil cooler. While on track, the gear oil leaving the oil cooler was over 20° F lower than the temperature of the gear oil in the differential case--even without the cooler-mounted fan switched on. Using the supplied fan, and ducting outside air directly to the cooler, will reduce the gear oil temperature even further. The MM IRS Differential Cooler will extend the life of the limited-slip unit, and keep the gear oil below Ford's maximum permissible temperature of 230° F.

The MM IRS differential oil cooling system includes

  • Premium quality Fluidyne oil cooler. The core has 20 rows, and is 11" wide by 8" tall by 2" thick
  • Gear-oil pump, with Viton diaphragm rated to 400°F
  • Electric fan pre-mounted to the cooler
  • 194° F thermo-switch to actuate the pump
  • 15' of -8 Teflon-lined stainless steel braided hose
  • AN hose fittings
  • Extra AN fittings (straight and 90°) to aid in unusual installation situations
  • Extra fitting for fitment with an aftermarket differential cover brace.
  • Check valve
  • Rubber isolation mounts for the cooler and pump
  • Complete installation instructions, with photos

Installation Notes

  • Removal of the IRS differential case from the vehicle is required for installation. This is a great opportunity to save on labor by installing other IRS performance parts at the same time, such as our differential bushings.
  • The installer is responsible for the positioning and mounting of the oil cooler, all wiring, hose routing, drilling and tapping the aluminum differential housing for the AN fittings and thermo-switch, and any desired air ducting.
  • A Tool Package is available that includes the thread taps and matching drill bits required for installation.