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Engine guides and mods

Changing Glow Plugs

How to change the glow plugs in your smart fortwo.

Modification Details




When Do The Glow Plugs Need Changing?

So far, I haven't seen any official schedule for changing the glow plugs on the smart. It would seem that
smart expect you to change the glow plugs when the error light comes on to tell you that there's a fault.

What normally happens is, when you turn the key to position 1, the glow plug light comes on and a few
seconds later it goes out. The light going out and staying out tells you that the glow plugs are OK. If,
after the engine has been started, the glow plug light comes back on, you have an error. 

The glow plug light should eventually go out again after a while.



So, the duration at which you change them is up to you. Personally, I'd recommend you change
them every 4th service instead of waiting for one to fail. The reason is simple. It's not unknown for
glow plugs to work for more than 100,000 miles, however, at that sort of age, you are going to have
a nightmare getting them out. It's far better to change them twice as often and for it to be a 20 minute
job each time rather than having to deal with seized or snapped glow plugs.

OBD Error Codes

As is the case, there are those of you out there who can't survive without your fault code readers.

P0380
P0381
U0106
U0307
U0407

P1481 (smart specific error code)

Glow Plug Removal - Theory

Open the engine cover to reveal your oil burning engine. At the back of the name
plate are 3 cutouts. Directly below these is where the glow plugs are located.



The diesel engine in a 451 and 450 are the same but a few things are packaged differently around it. These pictures
were taken of a 451 which has slightly easier access as the rubber conduit can be easily pushed out of the way.



Looking down the back of the name plate behind the indents you'll see the glow plug connectors.
This is plug 3, it the furthest left of the 3 plugs.



Here is plug 2 in the centre.



And finally, this is plug 1. They are labeled from right to left like the cylinders.



The connectors on the top pull off. They can be quite stiff but hooking something behind them helps.
Some glow plugs have a threaded connector, however, the smart's glow plug connections are smooth.
Below is a brand new glow plug. Generally they are less than £10 each.



With the electrical connection removed you should see the hexagon head. You'll need a long 10mm socket.



Use a ratchet with an extention and the long 10 mm socket, remove all 3 glow plugs and refit
3 new glow plugs with a dry thread using no more than 15Nm of torque to tighten them up.

Glow Plug Removal - Real Life

This is one of the most hit or miss jobs you can do. If it goes OK, it's a 20 minute job. If it goes badly then you are
in all kinds of trouble. The trouble comes in the form of the small thread and the fragile nature of the glow plugs.
If you snap a glow plug as you remove it, you are going to experience a world of pain. It really does require
the removal of the engine and remachining the head to remove the broken plug and rethread the hole.

With these stakes, it makes sense to prepare and try everything you possibly can to help them come out ok.

The main step is penetrating fluid such as:

PlusGas (UK)
GT85 (UK)
TryThis (UK)
Penetrene (AUS)
RP7 (AUS)
Liquid Wrench (US)
Kano Kroil (US)
PB Blaster PB16 (US)

Or you can make your own penetrating fluid from acetone and ATF (50:50).

Spray on your penetrating fluid of choice several times over a few days before you attempt removal.
You want to allow the fluid to penetrate as much as possible so apply some before you drive the car.

Driving the car heats up the engine and I'm sure most of you know, metal expands when it's hot.
The movement of the expansion allows the penetrating fluid to get further into the thread.

Just before you attempt to remove the glow plugs, go for a drive so the engine is hot.
Again, this expands the hole a tiny amount but it could be the difference between success and failure.

Set your torque wrench to 15Nm and tighten the glow plug, yes tighten. It's an old trick.
Now take a T handle with an extension and the long 10mm socket. You don't want to try and wind the plug straight out. You need to ease it out as if you were threading a hole with a tap. Go a quarter turn anticlockwise and an eighth turn back. Very much like 2 steps forward and 1 step back. You are doing this to allow the thread to clear. If you don't, the corrosion can clog the threads, create too much friction and cause the plug to seize or snap.

Fitting New Glow Plugs

On the box that your glow plugs came in, it will have the torque values.
You must NOT exceed this value. The tightening torque of a glow plug with a dry thread is 15Nm.
You can expect the plug to snap or the thread to fail at around 35Nm.

The initial response is to consider using copper grease on the threads to reduce the chances of
seizing next time. If you do this, it is very important to know that greasing the thread will reduce
the amount of torque required to set it OR SNAP IT. If you wet torque a glow plug with 15Nm of
torque, this will be very close to the 35Nm failure value of a dry plug.

If you really want to use copper grease on the thread, consider setting them at 8Nm and check tighten in 300 miles.

Does The Glow Plug Light Mean The Plugs Are Faulty?

Normally yes but not always. All the plugs are controlled by a glow plug controller (sometimes called a glow
plug relay, although it's more complicated than that). These controllers do fail but it is also worth checking
Fuse 9 on the 451 SAM unit (fuses will vary on other models). I will add more information in due course.

Change The Faulty Plug Or All 3?

In an ideal world, you want to save time and money just by replacing the 1 faulty plug.
In this instance it's not a great idea. You may as well change all 3 as you are there.
Glow plugs are usually quite well matched so when 1 fails, the others won't be far behind it.

Glow Plug Part Numbers

450 & 451 (45bhp only)

Denso DG-184 (Tolsen)
Beru GN015 (Tolsen)
NGK Y543J (Tolsen)
Champion CH228
Delphi HDS387 
smart A 660 159 02 01

451 (54bhp only)

smart A 660 159 04 01 (Rhoda)
NGK CZ108 (Gerard)
NGK CZ158 (Gerard)

Testing Glow Plugs

Take a look here.

Thanks to Tolsen whose information I read before creating this page.


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