Alarm Code 18
Out of serviceHigh Engine Coolant Temperature
Thermo King · reefer alarm · OEM code 18 · Thermo King
Protect the load now
The reefer's diesel engine is overheating. On most units this is a shutdown alarm, so treat it as a live load-temperature problem and not a maintenance item for next week.
CoolingTODO(verify): confirm alarm level and shutdown behaviour for the specific controller. On many configurations this is a shutdown alarm — the diesel stops to protect itself and the box begins warming.
LoadThe tractor is unaffected — this is the reefer's own engine. But if the unit has shut down, the load is warming right now. Get to a stop where you can check coolant and airflow, and call a reefer service line rather than restarting a hot engine repeatedly. Each restart on an overheating engine risks turning a thermostat into a head gasket.
Typical repair cost
- Parts
- $660–$2,530
- Labor
- 0.7–6 hr × $125–$210/hr = $88–$1,260
Provisional figures — pending verification against our receipt dataset.
Labor rate: provisional national placeholder — TODO(verify), not yet from our collected dataset. How we build these ranges.
Need it fixed
Phone-verified shops, with the date we last called each one.
What Alarm Code 18 means
This is a transport refrigeration unit alarm, not an engine fault code. It is reported by the reefer controller and has nothing to do with the tractor's engine ECM. The tractor may be perfectly healthy while the box is losing temperature.
Common causes
- Low coolant levelCheck it cold. Opening a hot reefer cooling system is a burn injury waiting to happen.
- Radiator or condenser coil blocked with debris, restricting airflow
- Failed or slipping belt driving the water pump or fan
- Thermostat stuck closed
- Water pump failure
- Coolant leak from a hose, the pump seal, or the radiator
- Coolant temperature sensor failed or wiring fault reporting high falsely
- Head gasket failure or internal engine problem
No frequency data yet. We have fewer than 5 verified repair receipts for Alarm Code 18, so we are not going to print percentages. Causes above are listed in no particular order. Had this fixed? Tell us what it turned out to be.
Technician note pending
A credentialed technician annotation for Alarm Code 18 has not been commissioned yet. Until it is, this page stays a draft and is excluded from our sitemap. We do not publish invented first-hand experience. How we verify content.
How a technician diagnoses it
- 1
Let the engine cool before opening anything. A pressurised reefer cooling system at temperature will scald.
- 2
Check coolant level at the expansion tank once cool, and look underneath the unit for evidence of a leak.
- 3
Inspect the radiator and condenser for blockage. On a reefer these are stacked in the same airflow path, so one blocked coil overheats both systems.
- 4
Check the belts for tension, glazing, and cracking. Confirm the fan and water pump actually turn when the engine runs.
- 5
Read the coolant temperature on the controller and compare with an infrared thermometer on the thermostat housing. A large disagreement points at the sensor rather than the cooling system.
Tool: Infrared thermometer
- 6
Watch for whether the engine warms normally then spikes — that pattern suggests a thermostat — versus running hot from cold start, which suggests airflow or coolant flow.
Spec: TODO(verify): thermostat opening temperature by unit engine model
- 7
Pressure test the cooling system if a leak is suspected and none is visible.
Tool: Cooling system pressure tester
- 8
Record the alarm time, box temperature, and setpoint before clearing. If the load goes out of range, that log is the documentation.
Parts and labour
| Part | Part number | Parts cost |
|---|---|---|
| Coolant and system flush | TODO(verify) | $40–$180provisional |
| Thermostat and gasket | TODO(verify) | $30–$150provisional |
| Belt set | TODO(verify) | $40–$200provisional |
| Water pump | TODO(verify) | $150–$600provisional |
| Radiator | TODO(verify) | $400–$1,400provisional |
| Labour | 0.7–6 hr | $88–$1,260 |
Labour priced at provisional national placeholder — TODO(verify), not yet from our collected dataset. How we build these numbers.
Can I keep running the load?
The tractor is unaffected — this is the reefer's own engine. But if the unit has shut down, the load is warming right now. Get to a stop where you can check coolant and airflow, and call a reefer service line rather than restarting a hot engine repeatedly. Each restart on an overheating engine risks turning a thermostat into a head gasket.
TODO(verify): confirm alarm level and shutdown behaviour for the specific controller. On many configurations this is a shutdown alarm — the diesel stops to protect itself and the box begins warming.
Find a shop that handles this
We call every shop before it appears here, and publish the date.
Sample records only — seeded to demonstrate the directory. None of these numbers has been called.
Phoenix, AZ · 24/7 · mobile service
Memphis, TN · Mon-Sat 7am-7pm · mobile service
Atlanta, GA · Mon-Fri 7am-6pm
Dallas, TX · 24/7 · mobile service
Codes that usually show up with this one
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