Thermostat failure signs

Thermostats are the watchdog of the engine’s cooling system, as they constantly monitor the temperature of the coolant and accurately regulate the coolant flow through the radiator to obtain and maintain the optimum engine operating temperature.

Thermostats, like any other part, don’t last forever. There are two scenarios for failing thermostats:

If the thermostat becomes stuck in the open position, there is continuous flow of coolant into the radiator causing the engine to run cold. Overcooled engines run inefficiently, which leads to increased fuel consumption and higher emission levels and engine parts enduring more wear. In addition, the car interior will not heat up properly.
If the thermostat becomes stuck in the closed position, the circulation of the coolant is blocked so the coolant cannot get to the radiator to be cooled which causes the engine to overheat.

The consequences of an “open failure” may be less catastrophic than those of a “closed failure” but are nevertheless undesirable for your customer. As not every case of thermostat ageing is clearly evident in the form of an obvious failure pattern, Gates recommends to service it preventively.

HOW TO INSPECT AND DIAGNOSE A FAILED THERMOSTAT?

The following signs indicate that a thermostat needs to be replaced:

Problem_Diagnosis_361x323_Thermostat_Leakage_Mounting_Surface

1. Leakage from the mounting surface

Appearance: Seepage, drips or large coolant bleed marks on or around the mounting surface or on the housing.

Cause: Improper thermostat installation or improper use of seals/gaskets or sealant.

Solution: In case of a recently installed new thermostat: carefully remove, check and re-install the thermostat. Strictly follow the torque specifications. Make sure seals/gaskets are in perfect condition and are installed correctly. When sealant is prescribed, clean the rims of the part and the mounting surface and apply new sealant evenly along the edge of the part. If the leakage is not the consequence of an improperly installed new thermostat, the thermostat must be replaced immediately.

Problem_Diagnosis_361x323_Thermostat_Rust_Corrosion

2. Rust and corrosion

Appearance: Rust and corrosion on the surfaces of the thermostat.

Cause: Contaminated coolant, non-compatible coolant or mixing coolants of different chemistries. Another possible cause may be a defective pressure cap causing air bubbles, accelerating the rust process.

Solution: Replace the thermostat. Thoroughly flush the cooling system before installing the new thermostat and refill the system with the correct vehicle manufacturer’s recommended coolant. Inspect the pressure cap and replace if defective.

Problem_Diagnosis_361x323_Thermostat_Deposit_Buildup

3. Deposit build-up

Appearance: Deposits, sludge and scale build up on the inside, clogging the thermostat and hampering proper functioning of its individual components.

Cause: Contaminated coolant, non-compatible coolant or mixing coolants of different chemistries.

Solution: Replace the thermostat. Thoroughly flush the cooling system before installing the new thermostat and refill the system with the correct vehicle manufacturer’s recommended coolant.

Problem_Diagnosis_361x323_Thermostats_Mapcontrolled

4. Map-controlled thermostats

Appearance: Map-controlled thermostats are a growing trend in OE. They have an electric heating resistor integrated into their wax element. Electrical heating of the wax element is triggered when the engine is exposed to specific load conditions and the engine management system anticipates an increase in waste heat. Map-controlled thermostats can dysfunction because of a “traditional open or closed failure” but also because of a damaged connection to or an electronic malfunction of the engine electronics control unit.

Solution: Check the plug for damage or corrosion and replace if defective. If this does not solve the problem, check the fault codes of the engine management system. Also check the thermostat for the traditional failure patterns mentioned previously and replace where necessary.