Short answer
TO-4 is a Caterpillar specification for transmission and drivetrain oil used in powershift transmissions, final drives and wet brake compartments that contain friction material. It is sold in single grades such as SAE 10W, 30 and 50, while TO-4M covers multigrade oils for wide temperature ranges. Unlike the older TO-2 category, TO-4 oils are for drivetrain use only and are not engine oils.
What TO-4 is designed to do
Heavy equipment drivetrains rely on oil to cool and lubricate gears and bearings while also letting wet clutches and wet brakes grip and release predictably. TO-4 sets requirements for that balance of friction, along with wear protection and other properties, so that clutches engage consistently and brakes don’t slip or chatter.
Caterpillar’s own fluid for these compartments is Cat TDTO, which Caterpillar describes for Cat transmissions, final drives and axles that contain friction material and for wet brake compartments. Other oil companies blend fluids to the TO-4 requirement.
Single grades and TO-4M
TO-4 oils are offered as single viscosity grades. SAE 10W, 30 and 50 are the most common, and some suppliers also offer SAE 60. Each compartment and climate range calls for a particular grade, which Caterpillar lists in its machine fluid recommendations.
TO-4M is the multigrade version of the requirement, for equipment that must operate across a wide temperature range without seasonal changes. Products sold for TO-4M are typically multigrades such as 10W-40.
TO-4 is not engine oil
The older Cat TO-2 category allowed oils that could double as engine oils. TO-4 does not. Suppliers consistently state that TO-4 oils are for drivetrains only and must not be used in an engine.
The reverse matters too: putting engine oil or a generic gear oil into a compartment that calls for TO-4 can change clutch and brake friction behavior.
Finding the right grade for a machine
Caterpillar’s “Machine Fluids Recommendations” service publication, SEBU6250, lists fluids and grades by compartment and ambient temperature, and is revised periodically. The operation and maintenance manual for the specific machine is the other key reference.
TO-4 is also called for by some non-Caterpillar equipment builders. In every case, match the grade and specification to the manual, then confirm the current product data before ordering.
Frequently asked questions
Can I use TO-4 oil in my diesel engine?
No. TO-4 oils are drivetrain oils and are not intended for engines.
What is the difference between TO-4 and TO-4M?
TO-4 covers single-grade oils such as SAE 10W, 30 and 50. TO-4M covers multigrade oils intended for a wide operating temperature range.
Which SAE grade do I need?
It depends on the compartment and ambient temperature. Use Caterpillar’s SEBU6250 recommendations and the machine’s maintenance manual.
General maintenance information. Always follow your vehicle or equipment manufacturer’s requirements and the current product data. Questions? Email [email protected].
