If your TDI car is consuming water and not heating up… keep an eye on the EGR cooler!

When a car engine consumes coolant, the alarms go off, especially if dense white smoke comes out of the exhaust, an almost unmistakable sign of a head gasket problem. And it can be very expensive, as the coolant “leaks” into the combustion chamber, with disastrous consequences. You know the drill: engine overheating, excessive wear as coolant mixes with the oil…

But there is a fault that is causing many headaches, especially for owners of cars with a TDI turbodiesel engine from the Volkswagen GroupVolkswagen, which can lead us to think it’s a head gasket problem when it isn’t. I am referring to problems or leaks in the EGR cooler.

Coolant consumption: possible causes

The first thing to keep in mind is that the cooling circuit is sealed and should not have any leaks. Therefore, if your car is consuming coolant, there are only two possibilities: either it is losing it somewhere, or it is burning it.

Normally a coolant leak is not difficult to detect. It may be a hose, a pinhole in the radiator, leaks from the water pump seal… Very often it is even something as simple as the expansion tank cap itself.

But if our TDI is consuming coolant, we have ruled out a possible leak, and the engine is not overheating beyond normal, the car is not smoking and there are no signs of overpressure in the hoses, the first thing to check, before even considering opening the cylinder head, is the exhaust gas recirculation valve cooler, the famous EGR.

The EGR cooler: problems and solutions

The so-called EGR cooler is nothing more than a heat exchanger, although externally it does not look like a radiator. Through this exchanger circulate the exhaust gases to be recirculated – that is, those that will be reintroduced into the intake to reduce the oxygen content and, in this way, reduce the nitrogen oxides produced during combustion – and the coolant, which is the same one used by the engine’s main cooling circuit. The aim, as you may guess, is to lower the temperature of the exhaust gases being recirculated, in order to improve combustion.

When there is a small leak in the EGR cooler, which usually occurs due to the corrosion caused by the vapours of the recirculated gases, the engine will consume coolant. Normally the consumption will not be excessive. But, sooner or later, the warning light indicating that the coolant level is at its minimum will come on, and you will have to top up the expansion tank.

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If the crack in the EGR cooler is small, the coolant may simply evaporate as soon as it comes into contact with the heat given off by the exhaust gases. For this reason, the leak will not be visible with the engine running. Nor will we notice the symptoms that coolant entering the cylinders would cause, such as white smoke from the exhaust. But the engine will consume coolant as the kilometres go by, and you will have to top it up.

However, if the leak is large enough, the symptoms are very similar to those of a possible head gasket problem, to the point that they can be confused. For this reason it is advisable to check the EGR cooler first, since it is much simpler… and cheaper.

Normally the way to do this is to bypass the pipes that circulate the coolant through the EGR cooler. In this way the exhaust gases will not be cooled, which entails a very slight loss of performance. But you can keep driving and check whether the consumption disappears. If it does, the EGR needs to be replaced. If, once the cooler is bypassed, the engine still consumes water, that is bad news, and everything points to the cylinder head.

How much does it cost to replace the EGR cooler?

Some people add leak sealer to the coolant, and it has worked for them. But it is a risk that can cause greater damage, since if the sealer does not do its job and passes through the crack along with the coolant, it will end up inside the cylinders and can cause bigger problems.

There are also drivers who, after suffering many problems with the EGR cooler, have chosen to leave it bypassed and disabled. It does not pose a problem for the MOT as long as the opacity values measured during the inspection remain within the permitted limits, as is usually the case. However, you should know that your car will pollute more if this cooler is not working.

The best option, therefore, is to replace the EGR cooler. The price of this part for a 2.0 TDI engine is around 180 euros, to which labour must be added. In total, replacing the part may cost around 300 euros. That is between 8 and 10 times less than a cylinder head repair, to say nothing of it.

Related information of interest

• 10 tips to make your diesel particulate filter last longer
• Internal engine decarbonisation: everything you need to know
• What do a car’s warning lights mean?
• The most common faults in diesel engines