Engine Coolant Temperature High Shutdown

Common Symptoms

• Machine shuts down abruptly mid-cycle with SPN 110 FMI 0 displayed on the instrument cluster LCD
• Coolant temperature gauge is pegged in the red zone or reading above 230 degrees F before shutdown
• Engine will not restart, or restarts briefly and shuts down again within minutes
• Visible steam or coolant smell coming from the engine compartment
• Cooling fan is running at full speed just before or after the fault triggers
• Machine was working hard in high-ambient heat, tight quarters, or near concrete dust and chaff
• Yellow or red engine warning lamp illuminated on the cab dash before the full shutdown event

Probable Causes (Ranked by Likelihood)

• Radiator face blocked by chaff, plastic sheeting, concrete dust, or job site debris reducing airflow Very Likely
• Low coolant level due to slow leak at hose clamps, water pump weep hole, or radiator seam Very Likely
• Cooling fan drive belt slipped or broken, or fan clutch not engaging fully under load Likely
• Coolant temperature sensor out of calibration or failed high, triggering a false shutdown Likely
• Thermostat stuck closed, preventing coolant from circulating through the radiator Possible
• Water pump impeller worn or cavitating, reducing coolant flow at high idle Possible
• Head gasket failure or internal coolant loss causing air pockets in the cooling circuit Less Likely

Step-by-Step Diagnostic Procedure

1. Let the engine cool for at least 20 minutes before opening anything. Never open a pressurized radiator cap on a hot engine. Check the coolant overflow bottle first. If it is empty or low, you likely have a leak or the system has been pushing coolant out under high heat.

2. With the engine cold, check the radiator cap seal and pressure rating. JLG specifies a 13-15 PSI cap on most PowerTech-equipped machines. A weak cap bleeds pressure early and lets the system boil at lower temps. Replace if the rubber seal is cracked or the cap is older than 3 years.

3. Inspect the radiator face and the AC condenser in front of it. On construction sites, plastic wrap, cardboard, chaff, and concrete dust pack into the fins fast. Use compressed air blown from the engine side out, or a low-pressure water rinse. If the fins are more than 30 percent blocked, that alone can trigger SPN 110 FMI 0.

4. Check the fan belt tension and condition. On Deutz and PowerTech platforms, belt deflection should be no more than 3/8 inch under moderate finger pressure. A glazed or cracked belt will slip under load and cut your fan speed significantly.

5. With the engine at operating temperature, watch the coolant temperature on the instrument cluster LCD or through JLG Analyzer software via the data link at the cab dash. Normal operating range is 180-210 degrees F. If the sensor reading climbs steadily past 215 degrees F with no load, suspect the thermostat or water pump. If it jumps erratically or reads 230 degrees F at idle with a cool radiator hose, the coolant temperature sensor itself may be faulty.

6. Pull the fault history using JLG Analyzer software via the data link at the cab dash. Confirm the SPN 110 FMI 0 is a genuine overtemp event and not a sensor rationality fault. A FMI 3 or FMI 4 alongside this code points toward a wiring or sensor problem rather than true overheating.

7. If coolant level is correct, fan is spinning, and radiator is clean but the machine still shuts down, perform a cooling system pressure test at 15 PSI for 10 minutes. Any drop indicates a leak. Also pull the engine oil dipstick and check for a milky or foamy appearance, which signals head gasket failure and requires immediate teardown. This step and beyond requires a shop visit.

8. Clear the active fault using JLG Analyzer software via the data link at the cab dash after repairs are made. Do not just cycle the key and assume the fault is gone. Verify the coolant temperature reads in the normal band under load before returning the machine to service.

Frequently Asked Questions