Broken candle - what's next?

The winter season is approaching, and with it a difficult time for owners of old diesel cars. Among the many possible malfunctions, one of the most common and difficult to fix is ​​the malfunction of glow plugs. To make matters worse, when removing damaged plugs, it is easy to strip their threads, which in practice leads to costly disassembly of the head. However, does a broken candle always mean ruin for our wallet?

How does it work?

The function of glow plugs in CI (diesel) ignition engines is to heat the air in the prechamber or combustion chamber so that the mixture can spontaneously ignite. These elements work only when starting the engine (in older types of diesel engines), as well as for a short time when driving with a cold engine (in newer solutions). Due to the peculiarities of their work, glow plugs are most often used in the winter season. It is also then that the most common damage occurs. Not surprisingly, many diesel car owners are now choosing to replace worn-out glow plugs.

How to replace and what to look for?

It would seem that a simple operation to unscrew the candles can cause many problems even for experienced people. It often happens that the candles cannot be unscrewed due to the fact that they are stuck. Any attempt to break the resistance by force may cause the threads to break when unscrewed. Worse, there is no rule for this and - attention! - in many cases completely independent of the actions of mechanics.

Moreover, in some car models the risk of such a situation is much higher than in others. What cars are we talking about? This happens, among other things, in Mercedes (CDI), in Toyota with D4D and Opel units (DTI and CDTI). In the case of these models, the breakage of glow plugs occurs, among other things, due to the use of long and thin threads (M8 or M10).

What does it mean to break a candle for a vehicle owner? First of all, you need to disassemble the head, and then remove the remnants of the candle. Consumption? In the case of newer diesels, even more than PLN 5…

Hope for specialized tools

Luckily for anyone who's had an unexpected "adventures" with glow plugs, there is a solution on the market that allows you to unscrew the plugs with special tools without removing the head. The tools are adapted to specific engines (different nozzles). When we don't have to dismantle the head, repairs can even be ten times cheaper: the cost of removing one glow plug is about PLN 300-500 net. This method has another valuable advantage: a mechanic with a set of tools is mobile and can easily reach the customer. In practice, you do not need to transport a wrecked car on a tow truck, which significantly reduces costs and increases the level of such a service.

Before screwing in a new one

After you have successfully removed the damaged spark plug, you need to clean the hole in the head for the spark plug filament. Then mill the spark plug socket in the head. Sometimes there are problems with the thread in the head: stuck candles are often damaged. In this case, correct the thread with a tap in the head. If there are no signs of damage on the threads, then before reassembling it should be thoroughly cleaned, and the threads of the spark plug should be lubricated with special grease. Failure to do so may result in baking. The spark plug itself is tightened with a torque wrench, with the torque recommended by the manufacturer (usually 10-25 Nm). The final step is to check the tightness of the tightening.