Glow plug light staying on

[johnsco]

Before you crank the engine, there is air in the cylinder, but no fuel.
Depending where the piston is in any of the cylinders, there may be a lot of air in the cylinder or very little ... Piston at top or bottom of stroke.
As soon as you crank the engine, the air that has been surrounding the glow plug is swept out of the exhaust valve and a new cold charge of air/fuel mixture is drawn in.
The glow of the glow plug helps to initiate the ignition of this mixture as it is heated by the adiabatic compression of the compression stroke of the engine.
It is the adiabatic compression that heats the volume of the air/fuel mixture.
The glow just gives it that little bit of extra help on a cold engine.

 

[walsi]

Here you go and this is straight from beru's website
Diesel engines are self-igniting, or in other words:
the injected fuel ignites without an ignition spark being
necessary. The work cycle is triggered in three stages:
1. Pure air is sucked in first.
2. This air is compressed to 30–55 bar – heating it up to
700–900 °C.
3. Diesel fuel is injected into the combustion chamber.
The high temperature of the compressed air triggers selfignition,
the interior pressure rises and the engine
performs its work.
Compared to gasoline engines, self-igniters require more
elaborate injection systems and engine structures. The first
diesel engines were not particularly comfortable or fast
drive units. When cold, the hard combustion sequence
made them very loud. They were characterised by a higher
performance weight, a lower performance per litre of
capacity and poorer acceleration behaviour. All of these
disadvantages have been eradicated by continual development
of the injection technology and the glow plugs.
Diesel is now regarded as an equal or better drive source.
Cold starts are all starting procedures in which the engine
and the medium are not at operating temperature. The
lower the temperature, the worse the conditions for fast
ignition and complete, eco-friendly combustion. In order to
ensure that the start does not take an inordinate period of
time or may indeed be impossible at lower temperatures,
aids are used to support the cold start. They compensate
the poorer starting conditions and initiate the punctual
and even ignition for stable combustion.
One component of the cold start support is the glow plug.
Thermal energy, generated by electricity, flows into the combustion
chamber to create the ideal ignition conditions for
the injected fuel. If an engine has a divided combustion
chamber, it is indispensable as a cold start aid in order to
ensure starts in frequent temperature ranges of 10-30 °C.
Due to the considerable deterioration of the start quality
at temperatures below freezing point, the glow plug is also
used for diesel engines with direct injection.

 

[walsi]

And another piece that says the same thing

Warm the Engine

• The most important function of the glow plug is to help warm the engine during cold periods. The diesel engine requires a lot of heat to operate consistently, as the diesel fuel will only fire if it is compressed heavily. This isn't a problem during warm periods or if the engine has been running awhile. However, if your diesel engine has been sitting around in cold weather for a long period of time, the engine block will get very cold. The cold engine block will suck up all the heat when you try to start the engine, causing it to struggle to start. A glow plug sticks just a bit out into the firing chamber. It will use battery power to heat itself up excessively, which will then cause the rest of the engine block to warm up. A glow plug can cause the engine block to heat to 800 degrees Celsius, greatly improving the engine's ability to start.
  
  

Reduce Emissions

• Diesel engines create a whitish blue smoke while they burn. This is caused by the burning diesel fuel creating fumes which are harmful to the environment. Glow plugs help reduce these emissions by up to 49 percent by creating a more efficient burning environment. With a warmer engine, the fuel will be burned more easily and will be "optimized," meaning it will be burned more smoothly and fully, eliminating much of the smoke after-affect of running a diesel engine. This is because the glow plug will still be incredibly hot after starting the engine. It will slowly cool down as the engine drives, but the extra heat caused by the cooling plug as well as the remaining heat left from heating the engine block will help the fuel burn more efficiently than it would otherwise.
  
  

 

[a111r]

And another piece that says the same thing

Warm the Engine A glow plug sticks just a bit out into the firing chamber. It will use battery power to heat itself up excessively, which will then cause the rest of the engine block to warm up.
A glow plug can cause the engine block to heat to 800 degrees Celsius, greatly improving the engine's ability to start.

 

[nessa20]

please help 110cdi 2.2 will not start after i ran out desil

hello im new to here my 2000 mrec 110cdi 2.2 ran out of desil i was just keeping it running i have been un well so its not movrd much in a year every time i went out it started straight away still good engine 78,000 miles i drove it for me around the corner as i new was not lot fuek in it , got it home on drive now ofcourse battery was flat had it on charge over night its turning over sounds normal the squiggly glow light is still on as long as im trying and ive sat there its still orange all other dash lights have gone out do you or anyone think its glow plug , i dont want to get conned into paying more money to fix it than i need to garages in my arrea at not that honest, please anyone one any help id be very greatfull vanessa

 

[picopro19k78]

I bought my ML270Cdi last week and the G Plug light goes out, then I start the engine (as per owners handbook) and then it comes on again for around 20-30 seconds and then goes out again. It doesn't come on again even of you stop the engine and go shops etc. When you restart it doesn't stay on again unless the engines gone cold.
I wouldn't say I'm not concerned but the car has an MB service history and has only done 75000 miles and is 13 years old. I expect that either there is a problem with one of the G plugs, low voltage somewhere or something but it is strange that it goes out and stays out so must be only during starting.
I guess it is something to worry about when it stays on.
Oil pressure lights, particularly on older cars, go out once the pressures reached, not during pressurisation.
Just my thoughts.

 

[Trickythemerc]

My 311 CDI Sprinter with 400k on it has a couple of duff glow plugs and still fires up at minus 5c it coughs a couple of times and then runs like a swiss watch.