Monitors and controls transfer oil temperature during high-load continuous driving to protect the transfer unit.

 

 

 

 

 

 

■Product Overview

• On the GR Yaris, the transfer system switches to 2WD during continuous high-load driving to prevent overheating.
• The HKS TRANSFER OIL COOLER helps maintain lower transfer oil temperatures, extends oil life, and protects the transfer unit.
  For vehicles equipped with the Transfer Protection Cancel Program, full-time 4WD is available even during circuit driving by disabling the limp mode, which switches to 2WD. *(Using the cancel program may void the vehicle’s warranty. Please check your warranty terms.)

 

Vehicles equipped with transfer protection control cancellation program

• Japan model: Jun/2025 -

※Vehicles manufactured from Aug/2020 to Dec/2020 do not feature Transfer Protective Control. 
For details, please contact the store where you purchased the vehicle.

 

 

 

 

■Components

 

 

■Features

• The dedicated pipe-type cooler ensures the transfer oil is cooled without affecting engine coolant, engine oil, or I/C cooling performance. The bracket fixing the cooler is designed to avoid obstructing airflow to the radiator and intercooler.
• HKS uses a high-load, high-flow electric oil pump, controlled by a dedicated pump controller. If the pump is operated when the oil temperature is low (high viscosity), the overcurrent protection control puts it in standby mode and automatically restarts once the oil temperature reaches an appropriate level. It’s recommended to operate the pump when the oil temperature is above 60°C to prevent overloading.
• For vehicles equipped with a transfer protection control cancellation program, selecting the TRACK mode within 1 minute of engine startup automatically activates the pump. The pump's operating status can be checked on the controller display. The kit includes wiring from the power source to the electric pump.
• The transfer oil outlet uses a specially designed banjo-type attachment that is resistant to impact damage. The banjo bolt has a PT1/8 plug hole, allowing for oil changes without removing the bolt, and can also be used as a temperature sensor mounting hole.

 

 

■Pump Controller Function

• The pump controller has the following operating modes and functions.
• Operating modes
  • AUTO mode (for vehicles without a transfer protection control cancellation program)
  • FULL AUTO mode (for vehicles with a transfer protection control cancellation program)
  • MANUAL mode (for maintenance)
• Current value monitoring function
  • When the pump current is above the rated value, it goes into standby mode. During standby, it operates the pump for 3 seconds every 30 seconds to monitor the current value
• Overcurrent protection function
  • Transfer protection control cancellation function (only valid for vehicles with a transfer protection control cancellation program)
  • The transfer protection control cancellation function can be used by connecting the vehicle's "4WD mode select switch" connector to the pump controller.

 

 

■Usage notes

• This product is designed for circuit use where transfer oil temperatures can rise significantly. For daily driving where transfer oil isn’t heavily loaded, please keep the pump turned off.
• Even on track, avoid operating the pump when the oil temperature is still low, as this can put excessive load on the pump and piping. Use it only when oil temps are around 60°C or higher.
• If using AUTO or FULL AUTO mode and the pump frequently starts and stops, it means the oil temperature is too low. In such cases, avoid long-term use to prevent damage.
• Please use stock transfer oil or HKS G900 75W-90 gear oil. Do not use oil thicker than 75W-90, as they can overload the system.
• The transfer protection control cancellation function only works on vehicles equipped with the appropriate program. If your vehicle doesn’t have this program, do not connect the “4WD mode select switch” connector — doing so will disable 4WD.
• Some vehicle modifications are required for installation:
  • Both models may also require trimming of bumper air ducts or undercover ducts.
  • GR Yaris: Radiator upper air guide plate, radiator air guide RH, engine undercover (duct)

 

 

Point!

 

 

■Driving test data of GR Yaris at Fuji Speedway Racing Course

 

• The test was terminated when the oil temperature increased to approximately 150°C, although the oil temperature is still rising without the transfer oil cooler installed.
• The test was terminated when the oil temperature rise settled at around 100°C with the transfer oil cooler installed.
• Based on these results, estimating the temperature at which the oil temperature becomes stable after further laps, the temperature difference with and without the transfer oil cooler is expected to reach about 50°C.　With the transfer oil cooler installed, the oil temperature can be stabilized at about 100°C even after continuous driving.

*The above information is based on in-house testing.