LOST JEEPS :: View topic - Quick Question about Glow Plugs

Will the engine suffer from damage if the vehicle is started before the glow plug light goes off?

Glow plugs just warm the air in the intake manifold so that it can reach compression combustion temperature faster. This decreases starter cranking time to start up, but our rigs will start without them if the temp isn't to ridiculous. Compression cycling will also raise combustion temps.

That sounds like a heating grid. My understanding of a glow plug... it goes straight in the combustion chamber, and warms THAT up so the engine will start easier.

Glow plugs provide a point of temperature within the combustion chamber that is way beyond the flash point of the fuel, so that no matter what the temperature of the air in the cylinder is, or what the temp of the combustion chamber is, a flame front can start. In this sense they are analogous to a spark plug, which does not electrify or heat the entire air/fuel charge. They don't heat the air or the chamber in toto, nor do they affect the viscosity of the fuel in any way.

Many diesel engines (my Unimog for example) have no glow plugs, and they usually start just fine. But it's a more reliable start with them, especially at very low temperatures.

I think that the biggest drawback to ignoring the glow plugs or to not having them is that unignited fuel washes the cylinder walls and gets down into the oil, eventually reducing its effectiveness. It also reduces your battery life, since it takes more cranking than if the glow plugs were working properly.

OK, so when my mom ignores the glow plug light (as always), I don't have to worry about anything?

Great. I didn't realize what that delay in starting was.

Marlon_JBT wrote:

OK, so when my mom ignores the glow plug light (as always), I don't have to worry about anything?

Great. I didn't realize what that delay in starting was.

I'd worry more about her ignoring the turbo cool down time.

Author:	Marlon_JBT [ Sun Jan 14, 2007 1:46 am ]
Post subject:	Quick Question about Glow Plugs
Will the engine suffer from damage if the vehicle is started before the glow plug light goes off?

Author:	Weegie5 [ Sun Jan 14, 2007 2:00 am ]
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My understanding is: if you don't wait for the glow plugs to turn off, you run the risk of burning fuel that may be too viscous (especially in cooler temp biodiesel). Heating the fuel up with the glow plugs reduces its viscosity (resistance to flow). Without the glow plugs doing their job, the higher viscosity fuel doesn't burn completely, which will leave deposits on the walls of the cylinders over extended periods of time. This is very bad. Doing it on an infrequent basis probably isn't too bad, but don't make a habit of it.

Author:	FastTRX [ Sun Jan 14, 2007 2:20 am ]
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I've always wondered the same thing...although I don't own a CRD or a diesel. My buddies all drive diesel trucks and I've been around many duramax's....and always wondered what the effect of starting before the glow plug light goes off will be. This occurs even in the summer when the temp. is up??

Author:	TDI4BY [ Sun Jan 14, 2007 3:05 am ]
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In my experience with the CRD it will not crank until the light goes out. Now with that being said it is a very quick period of time. Try it. get in and just crank the key. it will pause and then crank. The glow plugs cycle very fast

Author:	RFCRD [ Sun Jan 14, 2007 9:21 am ]
Post subject:	Re: Quick Question about Glow Plugs
Marlon_JBT wrote: Will the engine suffer from damage if the vehicle is started before the glow plug light goes off? No, the light will cycle quickly (in most cases) and it is believed the glow plugs remain "on" past the light cycle to assist in combustion while the engine is cold as part of the emission control function.

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Author:	spoonplugger1 [ Sun Jan 14, 2007 10:26 am ]
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Glow plugs just warm the air in the intake manifold so that it can reach compression combustion temperature faster. This decreases starter cranking time to start up, but our rigs will start without them if the temp isn't to ridiculous. Compression cycling will also raise combustion temps. Used to be you had to push down a metal button, or hold your thumb over a metal button, with a heating element under the button, while you turned your key in the direction ususally used for Acc. position and keep it there till you burned your thumb, which told you that the glow plugs were hot enough. We also used to have metered ether injection systems for the same purpose, but they caused undo damage to the engine due to oil washoff of the ether solvent action and a huge combustion knock due to the type of fuel used.

Author:	Marlon_JBT [ Sun Jan 14, 2007 12:12 pm ]
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spoonplugger1 wrote: Glow plugs just warm the air in the intake manifold so that it can reach compression combustion temperature faster. This decreases starter cranking time to start up, but our rigs will start without them if the temp isn't to ridiculous. Compression cycling will also raise combustion temps. That one is hard to believe... That sounds like a heating grid. My understanding of a glow plug... it goes straight in the combustion chamber, and warms THAT up so the engine will start easier.

Author:	CATCRD [ Sun Jan 14, 2007 12:17 pm ]
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Marlon_JBT wrote: That sounds like a heating grid. My understanding of a glow plug... it goes straight in the combustion chamber, and warms THAT up so the engine will start easier. That's correct, they warm the combustion chambers directly.

Author:	greiswig [ Sun Jan 14, 2007 1:17 pm ]
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Glow plugs provide a point of temperature within the combustion chamber that is way beyond the flash point of the fuel, so that no matter what the temperature of the air in the cylinder is, or what the temp of the combustion chamber is, a flame front can start. In this sense they are analogous to a spark plug, which does not electrify or heat the entire air/fuel charge. They don't heat the air or the chamber in toto, nor do they affect the viscosity of the fuel in any way. Many diesel engines (my Unimog for example) have no glow plugs, and they usually start just fine. But it's a more reliable start with them, especially at very low temperatures. I thin that the biggest drawback to ignoring the glow plugs or to not having them is that unignited fuel washes the cylinder walls and gets down into the oil, eventually reducing its effectiveness. It also reduces your battery life, since it takes more cranking than if the glow plugs were working properly.

Author:	oldnavy [ Sun Jan 14, 2007 2:53 pm ]
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greiswig wrote: Glow plugs provide a point of temperature within the combustion chamber that is way beyond the flash point of the fuel, so that no matter what the temperature of the air in the cylinder is, or what the temp of the combustion chamber is, a flame front can start. In this sense they are analogous to a spark plug, which does not electrify or heat the entire air/fuel charge. They don't heat the air or the chamber in toto, nor do they affect the viscosity of the fuel in any way. Many diesel engines (my Unimog for example) have no glow plugs, and they usually start just fine. But it's a more reliable start with them, especially at very low temperatures. I think that the biggest drawback to ignoring the glow plugs or to not having them is that unignited fuel washes the cylinder walls and gets down into the oil, eventually reducing its effectiveness. It also reduces your battery life, since it takes more cranking than if the glow plugs were working properly. That and the fact the engine does not fire till after the GP's lite up says it all, you are worrying about nothng. Our VW's didn't have the instant on GP's and the delay circuit to prevent starting w/o GP's and I would sometime switch between the gasser car and the diesel and forget to allow the GP's to warm up and would have a hard crank. I did it once at -2F and the car started and run on about the 3rd compression stroke, I was impressed with the TDI but realized it was as much the high quality 50 cetane fuel I was using at the time.

Author:	Marlon_JBT [ Sun Jan 14, 2007 10:45 pm ]
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OK, so when my mom ignores the glow plug light (as always), I don't have to worry about anything? Great. I didn't realize what that delay in starting was.

Author:	CATCRD [ Mon Jan 15, 2007 12:01 am ]
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Marlon_JBT wrote: OK, so when my mom ignores the glow plug light (as always), I don't have to worry about anything? Great. I didn't realize what that delay in starting was. I'd worry more about her ignoring the turbo cool down time.

Author:	Marlon_JBT [ Mon Jan 15, 2007 1:10 pm ]
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CATCRD wrote: Marlon_JBT wrote: OK, so when my mom ignores the glow plug light (as always), I don't have to worry about anything? Great. I didn't realize what that delay in starting was. I'd worry more about her ignoring the turbo cool down time. She's not new to turbochargers. And isn't a complete idiot.. Heck, I can't even drive stick... but she can.

Author:	Marlon_JBT [ Mon Jan 15, 2007 8:58 pm ]
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Update: I started up my Jeep today without waiting for the light to go off. Around 30ºF and I've NEVER had to wait that long before the engine finally decided to crank over and run. I will continue to wait for the light to turn off. There goes that theory.

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Author:	oldnavy [ Mon Jan 15, 2007 10:09 pm ]
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A lot of how the diesel starts (cold or hot) is quality of the fuel. A 50 cetane fuel will light off a lot easier then a 42 cetane fuel, but then it really doen't get as cold in Italy as it does in Germany or Montana for that matter.