The transmission fluid a Navistar International 4300 requires depends on the transmission installed. If it has an Allison automatic, use TES-389; if it’s a manual Eaton Fuller transmission, use a GL-4 gear oil such as 80W-90 or 75W-90. Always verify the exact spec for your year and model.
Understanding the 4300's transmission options
Automatic transmissions (Allison)
If your 4300 is equipped with an automatic transmission, the official spec is TES-389 from Allison. Using the proper TES-389 ATF helps ensure smooth shifting, clutch protection, and reliable performance across temperatures.
- Allison TES-389 Automatic Transmission Fluid (ATF) — the current recommended standard for Allison automatics used in Navistar 4300 trucks
Using the correct TES-389 fluid is essential for maintaining transmission performance and avoiding compatibility issues with seals and friction materials.
Manual transmissions (Eaton Fuller)
Manual transmissions in the 4300 typically require GL-4 gear oil. Common choices are 80W-90 or 75W-90, depending on climate and load. Do not use GL-5 unless the manufacturer explicitly allows it, as it can damage transmission components.
- 80W-90 GL-4 gear oil
- 75W-90 GL-4 gear oil
- 85W-140 synthetic gear oil (for extreme temperatures or heavy-duty use, if recommended by the transmission manufacturer)
Always confirm the exact viscosity and specification in the vehicle’s manual or through the transmission service bulletin, since some Fuller transmissions may have specific requirements.
How to confirm the correct fluid for your vehicle
To avoid guessing, follow these steps to verify the right fluid for your specific International 4300:
- Check the owner's manual and the transmission section for the recommended fluid specification.
- Identify the installed transmission model (Allison, Eaton Fuller, etc.) by the build sheet, VIN, or label on the transmission.
- Consult Navistar's service portal or contact the dealer or service center with your VIN to confirm the exact fluid spec for your truck's year and configuration.
In a pinch, do not mix fluids from different manufacturers and avoid using fluids not labeled for your transmission type.
Summary
For an International 4300, fluid choice is driven by the transmission. Automatic versions with Allison typically require TES-389 ATF, while manual Fuller transmissions usually call for GL-4 gear oil such as 80W-90 or 75W-90. Always verify with the owner's manual or a Navistar/Allison service bulletin for your exact model and year, and when in doubt, contact a dealer or service professional.