Here’s how to replace a thermostat on a 4 cylinder Honda 2.4L engine.
The thermostat is responsible for controlling the flow of the engine coolant as it circulates through the engine block. When the engine is cold, coolant does not flow. Once the engine warms up, the thermostat opens, circulating coolant to keep it at optimum operating temperature.
Sometimes the thermostat fails to open or close, causing the engine to run cold or overheat. The thermostat can also be replaced as a preventative measure when the engine coolant is drained, such as when changing a radiator or water pump.
Never work on the cooling system when the engine is hot. Drain the radiator through the bottom petcock valve and dispose of the coolant safely.
The thermostat is located on the engine block facing the front of the vehicle, under the intake plenum. There’s three 10mm bolts that need to be removed, along with the clip for the lower radiator hose.
Have a catch can located underneath the thermostat to catch remaining coolant in the block when the thermostat is removed. Replace the gasket and clean all mating surfaces with brake cleaner.
Replace the 10mm bolts and torque to 86 in-lbs using a torque wrench to avoid leaks. Replace the radiator hose.
Refill the cooling system with a 50/50 mixture of phosphate and silicate free Honda compatible engine coolant. Leave the radiator cap off and turn on the heater to cycle all the air through the system until the fans turn on and bubbles stop appearing.
This video was demonstrated on a 2004 Honda Accord 4 Cylinder. Procedure is the same for 2003-2012 Honda Accord and similar for the CR-V, Element, Civic, Acura RSX, and CSX.