What kind of transmission fluid does a 6.7 Cummins manual take?
The typical transmission fluid for a 6.7 Cummins manual is 75W-90 gear oil that meets GL-4 specifications, with some transmissions calling for MT-90 (75W-90) synthetic. Always verify the exact specification for your specific transmission model and year.
Understanding the transmission options that accompany the 6.7 Cummins
The 6.7-liter Cummins engine has appeared in Ram heavy-duty trucks with more than one manual transmission option over its production span. Fluid requirements depend not on the engine alone but on the particular manual transmission installed in your vehicle. In many markets, the manual option has been more limited compared to automatics, so owner manuals and transmission tags are the best sources for the precise specification.
Typical fluid options by transmission family
Below is a guide to the kinds of fluids commonly specified for the manual transmissions historically paired with the 6.7 Cummins. The exact requirement can vary by year, market, and the transmission model, so use these as a starting point and confirm with your manual or dealer.
- GL-4 75W-90 gear oil (synthetic is often preferred). This is a common specification for many manual transmissions used with diesel engines, including several variants found in the 6.7 Cummins lineup.
- MT-90 (75W-90) synthetic gear oil. Some transmissions list MT-90 as the preferred or optional fluid, particularly newer or revised manual designs.
- Avoid GL-5 gear oils unless the manufacturer explicitly approves them. GL-5 additives can be harsh on brass synchronizers and some older or specialty manuals.
In short, the safest approach is to match the fluid to your exact transmission model and year. If in doubt, consult the vehicle’s owner's manual, the transmission’s identification tag, or a Ram/Mopar dealer for the precise specification.
How to confirm the correct fluid for your build
To ensure you’re using the right fluid for your specific 6.7 Cummins manual, identify your transmission model and cross-check with official documentation. Start with these steps:
- Check the transmission model stamped on the side of the case or on the build plate, if accessible.
- Consult the owner's manual or service manual for the exact specification (GL-4 75W-90, MT-90, or another spec).
- Refer to the vehicle’s VIN-specific build sheet or contact a Ram dealer with the VIN for the exact transmission family and fluid recommendation.
- If performing a fluid change, use the recommended amount and verify maintenance intervals as prescribed by the transmission manufacturer.
Following these steps helps avoid using the wrong fluid, which can affect shifting performance and gear longevity.
Summary
The 6.7 Cummins manual transmission typically uses a 75W-90 gear oil conforming to GL-4 specifications, with MT-90 as an alternative on some models. Always verify the exact transmission model and year to confirm the correct fluid, and refer to the owner’s manual or a Ram dealer if you’re unsure.
