If your car has a heater plug, also known as a glow plug, then it’s a diesel engine. It’s a very important part of the engine that allows your car to start effectively, particularly on those cold mornings.
A heater plug, does exactly what it says, it heats. The part consists of a screw base with a wire coming from the end and a heating element on the top. This heating element will glow white hot (hence the name) to provide much needed heat to your engine.
The heat is important from cold starts as a diesel engine fires in a very different way to petrol. Instead of supplying a spark, small amounts of diesel fuel are compressed with air to the point where they com bust on their own as diesel fuel is a heavy oil that will not burn with a spark. In order for combustion to occur, it needs to reach a certain temperature and pressure. Which is fine once the engine is hot, however, on the cold mornings it just doesn’t provide enough heat on it’s own.
Purchasing diesel vehicles in the past meant you needed to be aware that when you turn the ignition on, the light in the picture above will come on for a few seconds. You must wait for that light to go out or you will be unable to start your vehicle. They weren’t wrong on the older diesel engines. However, today, this light flicks off within a second that you barely get a chance to notice it there. This is because technology has allowed more heat to be applied to the correct surfaces in a quicker and more efficient manner, however, the glow plugs are as just an integral part of the diesel engine today as it’s ever been.
So, you may be here because you suspect your glow plugs are faulty. To understand if they may be (the only definitive way to test is on a bench with them removed from your vehicle) then you only have to do a very simple test with your car. This test can only really be tested when your engine is cold so don’t do it after any kind of driving, in fact it’s best to do it first thing in the morning, when your car has been sat overnight.
The test simply involves turning your ignition on, not starting the engine, just switching your key to position 2. For cars with keyless start, you need to press start for a brief second rather than holding the button.
You’re looking for the heater plug light on the dashboard. It’ll look exactly like the image on the top of this page. If you’re having issues then this light will likely stay on for longer than normal. It may even flash or never go off. If it takes longer to go off than usual, try to start your car. If it starts, even if it’s a struggle or not, then you should still go and get them checked out. They’re an inexpensive part that can really have you stranded if you don’t look after them.
If your light doesn’t go out, or it flashes, this too can indicate a problem that needs looking into. However, there are occasions where flashing can indicate a different type of problem. The best thing to do is to give us a call and get it booked in. Our team will help you diagnose the problems.
As I’ve mentioned above, replacing your glow/heater plugs is generally inexpensive. This obviously can change depending on your car make, model and the number of cylinders you have. Your car will have 1 glow plug per cylinder.
The best thing to do in order to replace them is to get it booked in to us as soon as possible. Our team will take your car and test the plugs. This will involve a bench test to ascertain if they’re producing any heat at all. We do this as it could be 1 or all that have failed. If it’s only one then there isn’t necessarily a need to have them all replaced, however, they are a heating element and if 1 has failed, the chances are the others aren’t too far behind.
Once we’ve understood exactly which plugs have failed, we can provide you with a full price for replacement. The job usually takes an hour or less depending on your car however, it does need to be booked in through us first so we can ensure we have the correct parts in stock for your vehicle.
If you feel your car may just require some work with the heater/glow plugs then please just drop us a line. One of the team will get you booked in for an investigation. We’ve been working with diesel engines for over 20 years now, so we are very experienced in diagnosing many faults around the heater plugs on your car.