Gates 33959 thermostat for the 2021 Mack LR 6-cylinder 8.9L and other vehicles controls coolant flow to keep engine temperature in its working range. The valve in this engine coolant thermostat opens as the coolant heats up and closes as it cools.
- Green Stripe Heavy-Duty design withstands noise, vibration and harshness under the hood of trucks, buses, tractors and heavy equipment
- Heavy-gauge construction for corrosion resistance
- Quality-controlled factory calibration for accurate opening and closing regardless of pressure changes
- Temperature-sensitive heat motor gives consistent valve response for smooth performance and precise engine cooling
- Jiggle pins for air venting, plus two O-ring seals
Quick facts
- Part: Gates 33959 thermostat
- Also called: engine coolant thermostat
- Fits: 2021 Mack LR 6-cylinder 8.9L and other vehicles
- Material: Steel, Copper
- Condition: New
A thermostat stuck open or closed can show up as an engine that runs hot, warms slowly or swings on the temperature gauge. Before you replace the thermostat, rule out low coolant, a leak or a fan problem, because any of those can also make an engine run hot.
Fits
The vehicles covered include the 2021 Mack LR 6-cylinder 8.9L, the 2019 Mack MRU 6-cylinder 8.9L and the 2019 Mack Terrapro 6-cylinder 8.9L, and each takes one. Open the "Vehicles it fits" section to check your exact model and engine.
Specifications
Fit and size
- Quantity per vehicle: 1
- Height: 3.408 in
- Flange height: 2.158 in
- Height between flanges: 1.25 in
- Flange thickness: 0.08 in
- Sealing flange outside diameter: 2.873 in
- Bypass flange diameter: 1.62 in
- Valve outside diameter: 2.25 in
Build and materials
- Type: heavy-duty thermostat
- Design: bottom by-pass
- Start to open: 180°F (82°C)
- Material: Steel, Copper
- Seals: 2 O-rings
- Condition: New
- Country of origin: China
In the box
One thermostat with two O-ring seals. No gasket or installation tool is included.
Interchange: 4052-80 · 501-180
30318 · 14908 · 3940632 · 3968559 · 4930594 · 5274887 · 5284903 · 5337942 · 5478594
This part cross-references / interchanges with the following part numbers:
30318, 14908, 3940632, 3968559, 4930594, 5274887, 5284903, 5337942, 5478594, 4052-80, 501-180, 33959
Frequently Asked Questions
Does the Gates 33959 thermostat fit the 2021 Mack LR 6-cylinder 8.9L?
Yes. Gates 33959 fits the 2021 Mack LR 6-cylinder 8.9L, and the vehicle takes one. Open the "Vehicles it fits" section to check another model and engine.
Is a gasket included with this Gates thermostat?
No. Gates 33959 comes with two O-ring seals and no gasket. An installation tool is not included either.
At what temperature does this heavy-duty thermostat start to open?
This heavy-duty thermostat starts to open at 180°F (82°C).
What signs can a failing thermostat on a heavy-duty truck show?
An engine that runs hot, warms slowly or swings on the temperature gauge can point to a thermostat problem. A shop can test the thermostat to confirm.
What is the 33959 thermostat made of, and what design is it?
Gates 33959 is a heavy-duty bottom by-pass thermostat made of steel and copper, with jiggle pins for air venting.
