Coolant flange for your car

Effectively distributing the coolant with the coolant flange

The coolant circuit consists of different parts. A number of locations need cooling for different reasons. Therefore, even when there is only one central cooling circuit, it subdivides into several secondary circuits, supported by one or several coolant flanges installed in the engine.

Cooling circuits in the car engine

A water-cooled car engine has at least three circuits for the coolant:

• a main cooling circuit (large cooling circuit)
• a secondary cooling circuit ( small cooling circuit)
• a circuit for the interior heating

A car with a water-cooled oil cooler might contain an additional circuit. The main coolant circuit ensures permanent engine cooling under normal circumstances. The circuit connects the cooling channels in the engine compartment with the radiator in the car's front. The amount of coolant flow is regulated by the thermostat. The secondary coolant circuit directs the coolant from the radiator right back into the engine. Its task is bringing the engine up to its operational temperature as soon as possible. The secondary cooling circuit is regulated by the thermostat as well. The circuit for the interior heating is a manually switchable subdivision. The interior heating's construction, the so-called heat exchanger, is similar to the radiator, only smaller and located directly behind the bulkhead. Coolant flows through the heat exchanger, previously heated by the engine. A switchable blower behind the heat exchanger directs the engine heat into the interior.

Coolant flange: function and location

The coolant flange is a small, though important component connecting all circuits. In many cars the coolant flange is made of durable grey cast steel. These metal components hardly ever fail; nevertheless their gaskets require regular replacement. For reasons of costs and weight, coolant flanges are now made of duroplastic material. A coolant flange consists of several supports and connections for the large hoses in the car's cooling circuit. In addition to directing the coolant, the coolant flanges often contain other components such as temperature sensors or thermostat valves. Coolant flanges can be installed at different places in the car. Some are accessible, others buried deep within the engine compartment, which makes their replacement varyingly complicated.

Coolant flange defects

Normally, a coolant flange has a long life span. Changing temperatures in the engine compartment and vibrations can cause a coolant flange to crack or rupture. This defect is impossible to ignore. The engine temperature rises fast. Added coolant will flow out right away. A leaking cooling system is easy to repair, but must be addressed immediately. Otherwise, you risk serious engine damage. Typical damage following a leaking cooling system is a burnt cylinder head gasket or a piston seizure.

Coolant flange: repair

A coolant flange cannot be repaired. Attempts of sealing leakage with band aids or glue have only a limited effect. Such an emergency repair would only serve to patch up the cooling system long enough for a drive home or to the nearest garage. We strongly advise against radiator sealant agents. They only clog the cooling circuit and make the situation worse. Replacement by a new component is the only way to repair a defective coolant flange. This might mean a lot of work, but requires no technical/mechanical expertise. The original component is screwed onto the engine with two bolts. These are loosened and the hoses disconnected. Now the old coolant flange can be replaced by a new one.

Costs for a coolant flange

As the replacement is really cheap, stopgap repairs are not worth while. A new coolant flange is available starting at 5 EUR (± £4). A coolant flange wears due to old age. Therefore it is advised to always check the entire cooling system and replace additional components, such as:

• temperature sensors
• thermostat
• coolant hoses

These components are also very cheap. The hoses should be checked for deposits. If larger calcium deposits or other pollutants are found, a profound rinsing of the cooling circuit is recommended. The retail trade offers several suitable solutions.