Engine Coolant Temperature High Shutdown

Common Symptoms

• Machine shuts down without warning during heavy work or in hot weather
• Cab display shows E1418 or SPN 110 FMI 0 before or at shutdown
• Coolant temperature gauge climbs into the red zone on the cab display
• Engine will not restart immediately after shutdown, or restarts and shuts down again quickly
• Visible steam or coolant smell coming from the engine compartment
• Radiator screen or engine compartment packed with grass clippings, dirt, or debris
• Machine loses power or derate occurs just before the full shutdown event

Probable Causes (Ranked by Likelihood)

• Debris-clogged radiator screen or radiator core blocking airflow Very Likely
• Low coolant level due to slow leak or evaporation at the overflow tank Very Likely
• Failed or stuck-closed thermostat not allowing coolant to circulate Likely
• Cooling fan not spinning at full speed or fan belt slipping Likely
• Coolant temperature sensor failed high, sending false overtemp reading to ECM Possible
• Internal coolant leak causing air pockets in the system and reduced heat transfer Possible
• Water pump impeller worn or damaged, reducing coolant flow Less Likely

Step-by-Step Diagnostic Procedure

1. Let the machine cool down completely before opening anything in the cooling system. Hot coolant under pressure will cause serious burns.

2. Inspect the radiator screen and engine compartment door screen first. On landscaping machines this is the single most common cause. Clean all grass, dirt, and debris off the screen with compressed air or water. Check the radiator fins from both sides.

3. Check the coolant level in the overflow reservoir and in the radiator (only when cool). The overflow tank should be between the MIN and MAX marks. If it is low, top off with the correct CAT DEAC or ELC coolant and check for visible leaks around hoses, the radiator, and the water pump.

4. With the engine warmed up and the cap off the overflow tank, watch for coolant circulation. If the thermostat is stuck closed, you will see little or no flow when the engine reaches normal operating temperature. A stuck thermostat is a straightforward swap and costs very little.

5. Check the cooling fan. With the engine off, spin the fan blade by hand. It should turn freely with no wobble. Start the machine and verify the fan is spinning at full speed at operating RPM. On C3.3B and C3.4B engines, the fan is hydraulically driven. Low hydraulic pressure in the fan circuit can reduce fan speed. If the fan seems slow, a CAT dealer service tech with CAT ET will need to check fan drive pressure.

6. If coolant level is correct and the screen is clean but the code still fires, measure the coolant temperature sensor resistance. Disconnect the sensor connector and measure resistance across the sensor terminals. At room temperature (approximately 25 degrees C / 77 degrees F) a good sensor reads roughly 2,000 to 3,000 ohms. A reading near zero or open-circuit (infinite) means the sensor has failed and will need replacement.

7. Connect CAT ET via the J1939 service port to read live coolant temperature data and active DTCs. If CAT ET shows a normal temperature reading while the physical gauge is pegged high, the sensor wiring or sensor itself is the issue. If CAT ET confirms a real high temperature, focus on the physical cooling system.

8. If you have cleaned the screen, confirmed coolant level, confirmed fan operation, and replaced the sensor but the code returns, the water pump or a head gasket issue is likely causing the problem. That diagnosis requires a pressure test of the cooling system and is best handled by a CAT dealer service tech.

Frequently Asked Questions