Can we get rid of the thermostat in the cooling system?

Thermostat - useful information and advice to change yourself

Your car is overheating and the coolant temperature display lights up even though the coolant level is OK? Or does the engine take a long time to reach the optimum operating temperature? These could be symptoms of a defective thermostat. In our guide you can read about the task of the thermostat, the causes of possible defects and how you can change the thermostat in your car yourself.

Function of the thermostat

The cooling water is from the water pump Pumped through a circuit keeps the engine temperature constant. The Cooling water circuit includes the expansion tank, the engine including the cylinder head, the heat exchanger for the heater and the engine cooler. The cooling water consists of a coolant and frost protection for the winter.

The Thermostat measures and regulates the temperature of the cooling waterso that this keeps the engine at the correct temperature. Depending on how much heat the engine develops, it switches back and forth between the small and large circuits. A defective thermostat can no longer regulate the temperature and the car suffers Consequential damage. The To deceive is therefore essential.

Small and large cooling circuit

The cooling water pump is driven by the engine and pumps the cooling water through the circuit. When starting during the Warm-up phase is just that small cooling circuit activeso that the engine and cylinder quickly reach operating temperature. The optimal operating temperature is on most cars between 80 and 110 ° C. Only at this temperature does the car achieve optimum consumption and pollutant values.

As soon as the opening temperature is reached, the thermostat switches to large cooling circuit around. Here the cooling water also flows through the cooling water cooler at the front. The airflow cools the water before it flows back into the engine. The prevents excessively high temperatures and overpressure in the cooling system. If too much heat arises despite the large cooling circuit, the car switches one or more of them Cooling fan to. These are for example in summer at high outside temperatures or at high speeds needed.

The thermostat regulates the engine temperature while driving.

If the temperature of the coolant drops while driving, it can at any time back to the little one Change cycle.

Types and structure of thermostats

There are two types of thermostats: the "classic" thermostat with expansion element and the electric map thermostat. The basic functionality is identical for both types: One Spring plate is connected to a piston and opens or closes the inlet to the great cycle.

The Thermostat with expansion element uses an expanding fabric, usually some kind of wax. Depending on the temperature, this substance expands or contracts and thus switches back and forth between the cycles. So the way it works is mechanically.

The Map thermostat becomes controlled via the engine control unit. It has an electric actuator which opens and closes the circuit depending on the cooling water temperature.

Warning light for the radiator

In addition to the engine control lamp, most cars have a warning lamp for the temperature of the cooling water. The Coolant lamp indicates that the Cooling water temperature well above the setpoint lies. There is a risk that the cooling water will boil and cause damage if the cooling water pressure is too high.

In the short term this is not a problem because the Radiator cap a Pressure relief valve contains. This regulates the system pressure in the event of overheating and releases cooling water in the form of water vapor. The causes but you should fix it as soon as possible and replace defective parts, otherwise consequential damage can occur.

Defect in the thermostat - causes and consequences

The thermostat is not subject to wear, but it can mechanical defects suffer. Foreign bodies or rust in the cooling water can obstruct the spring plate. A defective seal allows cooling water to escape and the corrosion can damage other parts.

The wax can escape from the thermostat with an expansion element. A jammed piston would result and the thermostat no longer opens or closes. In the case of an electric actuator, the actuator can corrode due to a leak and jams. In all cases it is important to remedy the causes and change the thermostat before further damage occurs!

Thermostat no longer opens

If the thermostat is blocked when it is closed, the car drives permanently with the small cooling circuit. Continuing will cause too much heat and pressure prevails in the cooling system. The pressure relief valve prevents immediate piston seizure by regulating the excess pressure. However, overheating can damage parts such as the radiator hose and cylinder head gasket. In the worst case it comes to Engine failure due to defects in moving parts.

Thermostat no longer closes

If the thermostat is permanently open, it will run Car permanently in the large cooling circuit. This extends the engine's warm-up phase and ensures that it does its job when the outside temperature is cold optimum operating temperature not reached. This increases the wear on all parts of the engine.

In addition, this leads to legal problems with the General inspection. Without the operating temperature, the vehicle is TÜV approved bad emissions measure up. You have to find the causes and change the broken part so that the car can get a new badge.

Change the thermostat yourself - step by step instructions

You suspect one of the above-mentioned causes in your car and want to change the thermostat? Simply replace the worn thermostat according to our installation instructions.

To change the thermostat you will need the following Tools and aids:

  • Lift or pit
  • Set of socket wrenches
  • possibly additional keys depending on the car
  • a piece of hose
  • Container for collecting coolant
  • Coolant and antifreeze for topping up
  • funnel

1. Preparation

A lot of coolant leaks out when changing the thermostat. It is therefore advisable to at least partially drain this beforehand. You can do that too Change thermostat directly and to step 3 pass over, but then the liquid runs into the engine compartment and is more difficult to collect there.

Open the to drain the liquid surge tank in the engine compartment. Then look for that Cooling water drain valve under the car. This is best done on a lifting platform or pit. You may have to dismantle part of the paneling on the underbody to do this.

2. Drain the coolant

Plug in one Hose on the spout and set the container under. Now open that Valve and drain the cooling water. Catch the liquid as it is a hazardous substance. Then close the valve and reattach the panel. The thermostat can be changed from the engine compartment.

Tip: You have now drained the coolant. It is a good idea to change them right away, unless this was done recently. We have also created a guide that explains how to replace the coolant and antifreeze. Otherwise you can refill the cooling water after replacing the thermostat.

3. Find the thermostat housing and loosen it

You can now change the car's thermostat. Look in the Near the engine block after a coolant hose with a large socket. The thermostat is located in this sleeve. She is mostly with two screws attached, which are often difficult to access. Depending on the car, you may need a special key to access the screws. This could, for example, be a hexagon socket with a ball head. It may also be necessary to remove other interfering parts in order to change the thermostat.

Hire one container under the engine and loosen the lid of the thermostat. Some coolant can still leak out. The thermostat can be changed in this housing. Remove You that Thermostat and the seal of the lid. You should also replace the seal.

Note: If you have not drained the cooling water, a significantly larger amount of liquid will run out at this point.

Check the housing for damage. A failure of the thermostat can also result from damage to the housing. In the middle of the case there is a webin which the thermostat is located. If this breaks in your car, you will have to replace the housing with it.

4. Change thermostat

First change the Gasket of the thermostat cover and make sure that both thermostats are identical. Then put that Thermostat in the housing and reattach the housing to the motor. Pay attention to the Assembly that that Thermostat just inserted is and not canted. It should slide in without resistance. Do not work with force under any circumstances: In the event of mechanical damage, you must change the thermostat again immediately!

5. Assembly

After replacing the thermostat, attach the Screws of the housing again and drag this with the prescribed torque at. Do not use too much force here, otherwise the housing can be damaged. This danger exists especially with a plastic housing. Build too other parts that you dismantled to change.

6. Fill up the coolant and vent the coolant circuit

Changing the thermostat is complete. Now the car just needs it Coolant. If you change the coolant, make sure it is the correct liquid acts.

Fill in the Expansion tank full and waiting A minute or two. The level should drop noticeably as the liquid is distributed in the lines. If the Constant level remains, fill it back up to Max mark on.

The car's cooling system is working self-bleeding. All you have to do is start the car and the Let the engine warm up while stationaryso that the thermostat opens the large circuit. Observe All the time about that Level. This will decrease again as the coolant is now distributed everywhere. Top up if necessary to keep the fluid level always between min and max remains. When the level no longer changes, changing the thermostat and venting is complete.

Costs and effort change the thermostat yourself

Replace the defective thermostat in your car yourself with the help of our guide and save a lot of money. The Spare part costs depending on the car between 20 and 60 €. The Workload to change the thermostat is depending on the car half an hour to two hours.

Have the thermostat replaced in the workshop

Don't you dare to diagnose and change yourself? Then have the thermostat replaced in the workshop. Of course, there are higher costs here. The average will be to change the thermostat depending on the vehicle between 100 and 250 € calculate.

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