Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

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HOMESERVICE MANUALSMERCURY2010MARINER HYBRID, AWDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1455 (ENGINE COOLING SYSTEM (HYBRID))DIAGNOSIS AND TESTINGENGINE COOLINGSYMPTOM TABLE

2010 Mercury Mariner Hybrid, AWD

Symptom Table

2010 Mercury Mariner Hybrid, AWDSECTION Symptom Table

WARNING: This page is about a different car, the 2011 Mercury Milan, 2011 Lincoln MKZ, and 2011 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

SYMPTOM TABLE

Condition	Possible Sources	Action
Loss of coolant	Coolant hoses or tubes Hose clamps Coolant pump O-ring seal Thermostat housing gasket Thermostat housing Radiator Degas bottle Pressure relief cap Coolant pump leaking from weep hole Heater core Engine gaskets (may leak internally or externally) Cylinder block core plugs Cylinder head core plugs Auxiliary coolant flow pump Block heater (if equipped)	GO to PINPOINT TEST A .
The engine overheats	Low coolant level External engine coolant leak Airlock in system	GO to PINPOINT TEST B .
Pressure relief cap installation Restricted airflow through the A/C condenser/radiator Internal engine coolant leak Coolant condition/concentration Accessory drive components Non-OEM engine enhancement components Electric cooling fan Radiator Thermostat Cylinder Head Temperature (CHT) sensor Heater core Coolant pump Coolant flow restriction
The engine does not reach normal operating temperature	Low coolant level Thermostat Electric cooling fan always on CHT sensor	GO to PINPOINT TEST C .
The block heater does not operate correctly	Block heater power cable	CHECK continuity in all 3 power cable circuits. If any circuit measures more than 5 ohms, INSTALL a new power cable.
Block heater		CHECK the resistance of the block heater. If the resistance does not measure between 12.5 and 17 ohms, INSTALL a new block heater.
The electric cooling fan is inoperative in one or more speeds or does not operate correctly	Wiring Relays Fuses Fan Control (FC) module Cooling fan motor REFER to the INTRODUCTION -- FUSION HYBRID, MILAN HYBRID & MKZ HYBRID article.
The electric cooling fan stays on all the time	Wiring Relays	REFER to the INTRODUCTION -- FUSION HYBRID, MILAN HYBRID & MKZ HYBRID article.
Noisy electric cooling fan operation	Foreign material contamination Fan motor	REMOVE the foreign material from the cooling fan and shroud. TEST the system for normal operation. If still noisy, INSTALL a new cooling fan assembly.
Fan blade detached from fan motor		INSTALL a new cooling fan assembly.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.
• Brakes feel soft, pull hard to one side, or make grinding noises.
• The engine overheats, stalls repeatedly, or misfires under load.
• You are missing required tools, torque specs, or safe lifting equipment.
• You are not confident in the next step or safety outcome.