High Engine Temperature Shutdown Triggered

Common Symptoms

• Generator shuts down mid-run and displays code 18 on the RDC2 controller display panel
• RED fault light is illuminated on the panel after shutdown
• Generator cranks and starts but shuts itself off within a few minutes of running under load
• You can feel or hear the cooling fan running harder than normal before shutdown
• Generator runs fine during the weekly exercise cycle but trips when household loads are applied
• Coolant level sight glass shows low or empty if your model has a liquid-cooled engine
• Generator does not return to READY status after reset until the engine cools down

Probable Causes (Ranked by Likelihood)

• Blocked or restricted airflow around the generator enclosure, preventing the cooling fan from moving enough air across the engine Very Likely
• Low or depleted coolant level in the radiator or overflow reservoir on liquid-cooled models such as the Kohler 20RESCL or larger RESCL units Very Likely
• Cooling fan blade broken, loose, or not spinning due to a failed fan motor or sheared key on the fan shaft Likely
• Failed or stuck-open thermostat preventing coolant from circulating properly through the engine block Likely
• Coolant leak at a hose, fitting, or the water pump causing coolant loss over time Possible
• Faulty coolant temperature sensor or coolant temperature sender sending a false high-temperature reading to the RDC2 controller Possible
• Generator operating in an enclosure that has restricted ventilation due to debris, foliage, snow, or a nearby wall blocking exhaust airflow Less Likely

Step-by-Step Diagnostic Procedure

1. Start by pressing the OFF button on the RDC2 controller display panel and letting the engine cool completely for at least 30 minutes before you touch anything.

2. Walk around the generator enclosure and look for any obstructions within 3 feet of the intake and exhaust vents. Remove leaves, grass clippings, snow, or debris. Kohler requires a minimum clearance of 18 inches on the sides and 36 inches at the exhaust end.

3. On liquid-cooled models (RESCL, RCL series), locate the coolant overflow reservoir and radiator cap. With the engine COLD, remove the radiator cap and check the coolant level. It should be at the full line. If low, top off with a 50/50 mix of ethylene glycol antifreeze and distilled water. Look for signs of a leak, including white stains or wet spots on hoses and fittings.

4. Inspect the cooling fan visually. With the generator OFF and breaker locked out, look into the engine compartment and verify all fan blades are intact and the fan is firmly seated on its shaft. Spin the fan by hand. It should rotate freely with no wobble.

5. Check the air filter. A heavily clogged air filter can cause the engine to run lean and run hotter than normal. Remove the air filter element and hold it up to light. If you cannot see light through it, replace it.

6. With the engine cold, use a multimeter set to resistance (ohms) to test the coolant temperature sensor. Disconnect the sensor connector and measure resistance between the sensor terminals. A good sensor on most Kohler RES engines reads approximately 2,000 to 3,000 ohms at room temperature (around 70 degrees F). A reading of zero ohms (short) or infinite resistance (open) means the sensor has failed and may be sending a false high-temperature signal to the RDC2 controller.

7. If coolant, airflow, fan, and sensor all check out, the thermostat may be stuck closed. This is a moderate repair. Drain a portion of the coolant, remove the thermostat housing, and inspect the thermostat. A stuck-closed thermostat will not open when you place it in a pot of water heated to 180 to 195 degrees F on a stove. If it does not open, replace it. This step requires basic mechanical skill.

8. If none of the above steps resolve the fault, the RDC2 controller itself may be misreading the sensor circuit, or you have an internal engine issue such as a failing water pump. At this point, call a Kohler authorized service technician. Do not continue running the generator until the root cause is confirmed.

Frequently Asked Questions