Difference Between J20C & J20D Fluid

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Agricultural machines, such as tractors, require specific oils to properly lubricate the transmission's moving gear assemblies. In fact, tractors manufactured by John Deere need transmission oils designed for particular seasons, either warm or cold months. J20C and J20D transmission oils are both used in John Deere machines, but offer different lubricating properties.

Transmission Oil Basics

The moving gears within a John Deere machine transmission undergo a lot of friction as they provide speed changes to the engine. The transmission's metal parts need lubrication for smooth gear transitions, especially in colder weather. Cold weather makes transmission oil more viscous, creating more friction than necessary against the gears. A John Deere machine owner must place the correct oil viscosity within the transmission or expensive damage may occur from gears becoming stuck within their own lubrication.

J20C Fluid

J20C transmission oil offers a high viscosity meant for mild temperatures and hot days. As the outside weather and transmission heat up during daily use, the J20C oil will slowly lose viscosity as the temperature increases. However, the oil begins as a thicker substance at room temperature, resulting in a reduced viscosity over the day's temperature rise that still lubricates the transmission's gears effectively.

J20D Fluid

In contrast, J20D transmission oil offers a low-viscosity fluid at room temperature. This oil is considered a winter grade lubrication fluid. John Deere machine owners must place this type of oil within the transmission for the winter months. As the outside temperature drops, the transmission oil's reaction is to immediately thicken, effectively clogging the transmission's gears. However, J20D's initial low viscosity prevents gear clogging since it begins as a thin fluid and only thickens slightly, allowing the transmission to function in cold weather.


John Deere machine owners should not mix transmission oil types to create an all-season lubrication. Mixing the oils may result in costly damage to the transmission in extreme hot or cold weather. Make sure to remove all old oil from the transmission before changing to an alternative oil viscosity.

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