Isuzu NPR, NQR, NRR, GM, Mitsubishi FUSO, UD: Prevent Transmission Failure & Overheating Problems

There are three types of automatic transmissions in the Japanese imported midrange trucks.  This includes Isuzu’s NPR, NQR, NRR, FRR, and FTR as well as GM’s W3500, W4500, W5500 and W6500 models, Chevrolet’s W3, W4 and W5 trucks, Mitsubishi FUSO’s FE, FG, FH, FK, and FM trucks, and UD’s 1200, 1300, 1400, 1800, 2000, 2300, 2600 and 3300 trucks.

  1. Jatco (primarily found in ’98 and older smaller trucks)
  2. Aisian-Seiki (primarily found in ’99 and newer smaller trucks)
  3. Allison  (Allison transmissions are found in the bigger imported trucks)

The most common problem we are seeing is related to overheating that leads to transmission failure in imported trucks.  One cause is related to sludge build-up in the cooling system of the transmission.  It can be eliminated by flushing the cooling system with a good grade of transmission cooling system flush that can be purchased at your local auto parts store.  This is done by disconnecting the cooler lines of the transmission and flushing the lines and the cooler itself with a good grade of transmission flush.

Flushing the system, along with changing the fluids can extend the life of your transmission and should be done regularly.  It is important to change the fluid every 35,000 -40,000 miles even if you’re not experiencing problems.  Some people don’t ever change it, some people just change the oil and that results in transmission failure. 

The other problem that causes transmission failure from overheating is a malfunctioning electric fan or thermostat that controls the fan.  Some models are equipped with an electric fan on the transmission cooler.  It is very important to make sure this fan is working properly.  There is an easy way to check this:  when the engine is hot, visually see if this fan is running by simply looking at it.  Or you can short the thermostat wires that control this fan and make sure it is coming on properly.  You should check this immediately after pulling a heavy load to make sure the fan is coming on properly to avoid transmission failure.  Of course, the best way is to have it checked by a certified and fully trained professional.  It is easier and cheaper to replace a faulty fan and/or thermostat than to replace a transmission.

Go to to view our helpful videos about Mitsubishi Fuso, Isuzu NPR, NQR and GMC W-Series trucks.


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