Gates 33964 Engine Coolant Thermostat - Driver Side

Heavy-Duty Cooling Control

Gates 33964 is a heavy-duty engine coolant thermostat built for demanding cooling systems in trucks, buses, tractors, and heavy equipment. It uses a steel and copper construction with an O-ring seal and a bottom by-pass design to support stable coolant regulation in harsh underhood conditions.

Compatible With heavy-duty cooling applications where a 180°F thermostat is specified, including select truck, bus, tractor, and equipment platforms. Gates 33964 is built for buyers searching for a heavy-duty thermostat replacement that matches OE-style dimensions and bypass configuration.

Key Features

• Heavy-duty thermostat for engine coolant temperature control
• Bottom by-pass design for applications that require bypass flow management
• Steel and copper construction for durability in demanding service
• 180°F start-to-open temperature, also listed as 82°C
• O-ring seal type with no gasket required
• No jiggle pin weep hole and no installation tool included
• Gates Heavy-Duty Thermostat line is built for noise, vibration, and harshness found in commercial-duty environments

Product Details

Gates 33964 is part of the Green Stripe Heavy-Duty Thermostat line, a product line focused on commercial vehicles and equipment that operate under sustained load and vibration. The thermostat’s steel and copper build, 2.57-inch overall height, 2.12-inch sealing flange outside diameter, and 1.11-inch by-pass flange diameter help support proper fit in applications that call for this configuration. If you are replacing a thermostat on a truck, bus, tractor, or heavy equipment cooling system, this part number is a direct match for the specified heavy-duty design.

This part cross-references Motorad 4056-80 for the same application.

Common Problems It Can Address

• Engine running too cool or too warm due to thermostat wear
• Unstable coolant temperature in heavy-duty service
• Cooling system issues tied to a bypass-style thermostat mismatch
• Replacement needs for commercial vehicles with a 180°F thermostat specification
• Thermostat housing service where an O-ring sealed unit is required

Installation Notes

Verify the bottom by-pass configuration, flange dimensions, and opening temperature before installation. Clean the thermostat housing sealing surface thoroughly and inspect the O-ring seat for debris or corrosion. Because this design does not use a gasket or installation tool, confirm the correct seal placement and torque fasteners evenly during assembly.

For fitment-based searches, use Gates 33964 when looking for a heavy-duty engine coolant thermostat for truck, bus, tractor, or heavy equipment cooling systems. This thermostat is also commonly searched as Gates 33964 heavy-duty thermostat and Gates 33964 coolant thermostat replacement.

Quality Assurance

Gates manufactures the Green Stripe Heavy-Duty Thermostat line for commercial-duty cooling environments where durability and consistent temperature control matter. Part number 33964 is built to the listed material, seal, and dimensional specifications for application matching.