Kia Optima: Cooling System / Thermostat

Kia Optima DL3 2019-2025 Service and Repair Manual / Engine Mechanical System / Cooling System / Thermostat

Components and components location

Components

1. Water inlet fitting
2. Thermostat

3. Bypass hose
4. Heater pipe & hose assembly

Repair procedures

Removal and Installation

Disassembly of the thermostat would have an adverse effect, causing a lowering of cooling efficiency. Do not remove the thermostat, even if the engine tends to overheat.

Thermostat

1.	Drain the coolant. (Refer to Cooling System - "Coolant")

2.	Disconnect the radiator lower hose (A)

Remove the water inlet fitting (A) and thermostat (B).

Tightening torque :

18.6 - 23.5 N•m (1.9 - 2.4 kgf•m, 13.7 - 17.4 lb•ft)

Install in the reverse order of removal.

•	Install the thermostat with the jiggle valve upward.

•	When assembling the thermostat, place the thermostat on the housing with a protrusion of thermostat matching with a groove of the housing and install the inlet fitting. Be careful the thermostat doesn’t get out of the groove on the housing.

•	Clean surface on the rubber packing contact surface.

5.	Fill the engine coolant.

6.	Start the engine and check for leaks.

7.	Recheck the coolant level.

Heater Pipe

1.	Remove the intake manifold. (Refer to Intake and Exhaust System - "Intake Manifold")

2.	Remove the bypass hose (A).

Unfasten the heater pipe mounting bolts (B) and then remove the heater pipe.

Tightening torque :

19.6 - 23.5 N•m (2.0 - 2.4 kgf•m, 14.5 - 17.4 lb•ft)

Do not reuse the seal bolts.

4.	Install in the reverse order of removal.

5.	Fill the engine coolant. (Refer to Cooling System - "Coolant")

6.	Start the engine and check for leaks.

7.	Recheck the coolant level.

Inspection

Thermostat

Immerse thermostat in water heated to over 95°C (203°F), then heat for at least 3 minutes to check valve lift.

•	Do not use water below 95°C (203°F).

•	Do not directly heat unit as this will damage thermostat.

Check the valve opening temperature.

If the valve opening temperature is not as specified, replace the thermostat.

Valve opening temperature :

88 ± 1.5°C (190.4 ± 34.7°F)

Full opening temperature : 100°C (212°F)

Check the valve lift.

If the valve lift is not as specified, replace the thermostat.

Valve lift : 8 mm (0.3 in.) or more at 100°C (212°F)

Troubleshooting

Symptoms

Possible Causes

Remedy

Coolant leakage

•	From the thermostat gasket

Check the mounting nuts

•	Check the torque of the mounting nuts

•	Retighten the bolts and check leakage again.

Check the gasket for damage

•	Check gasket or seal for damage

•	Replace gaskets and reuse the thermostat.

Cooled excessively

•	Low heater performance (cool air blows-out)

•	Thermogauge indicates 'LOW'

Visually check after removing the radiator cap.

•	Insufficient coolant or leakage.

•	After refilling coolant, recheck.

KDS check&Starting engine

•	Check DTCs

•	Check the fan motor performance as temperature varies.

•	Check connection of the fan clutch or the fan motor.

※ If the fan clutch is always connected, there will be a noise at idle.

•	Check the engine coolant sensor, wiring and connectors.

•	Check the fan motor, the relay and the connector.

•	Replace the components.

Remove the thermostat and inspect

•	Check if there are dusts or chips in the thermostat valve.

•	Check adherence of the thermostat.

•	Clean the thermostat valve and reuse the thermostat.

•	Replace the thermostat, if it doesn't work properly.

Heated excessively

•	Engine overheated

•	Thermogauge indicates 'HI'

Visually check after removing the radiator cap.

•	Insufficient coolant or leakage. ※ Be careful when removing a radiator cap of the overheated vehicle.

•	Check air in cooling system.

•	After refilling coolant, recheck.

•	Check the cylinder head gaskets for damage and the tightening torque of the mounting bolts.

KDS check&Starting engine

•	Check DTCs

•	Check the fan motor performance as temperature varies.

•	Check if the fan clutch slips.

•	Check the water pump adherence or impeller damaged.

•	Check the engine coolant sensor, wiring and connectors.

•	Check the fan motor, the relay and the connector.

•	Replace the fan clutch, if it doesn't work properly.

•	Replace the water pump, if it doesn't work properly.

Immerse the thermostat in boiling water and inspection.

•	After removing the thermostat, check it works properly.

※ Check the thermostat opens at the valve opening temperature.

•	Replace the thermostat, if it doesn't work properly.

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