bad for glow plugs?

[GSS]

Is it bad for the glow plugs (or anything else) to start the tractor while they are still "lit"? My Cub Cadet manual says to wait til the glow plug light goes out before turning the engine over. I however am not that patient, as they are still on after a minute or so...

My old IH656 has the glow plug button, so you could decide when was long enough to run the glow plugs and turn them out before hitting the starter.

Thanks.

- G

 

[RoyJackson]

I'd be a little concerned about starting when the glow plugs are hot. I suppose it could be possible to damage a piston (burn a hole in it)...but I am guessing there.
Has your glow plugs always stayed on that long? Normally 20-30 seconds is about it. Does the glow plug light go off when you crank the engine?
My Deere is set up so you turn the key counterclockwise to turn on the glow plugs...hold the key in that position and wait 10-20 seconds...then turn the key clockwise to crank the engine. With that system, the plugs are turned off when cranking.
What does your manual say about starting with the glow plugs?

 

[GSS]

I just got it last Sat, so I don't have anything to compare it to. Yes, the light goes out when you crank it, but the glow plug key position is clockwise from stop and clockwise from there is the starter position. I'll have to look at the manual again, but I don't recall any warnings about starting it before the light goes out.

Thanks.

 

[EdKing]

The way my Long works is when you first turn the key on the glow plugs come on for a short time, then go off. When you turn the key to the start posistion, they come back on while you are cranking the engine, then go back off when you let the key go back to the run posistion. In really cold weather you can make them stay on longer by turning the PTO switch on (which prevents the starter from engaging) and then turning the key to the start posistion and holding it there for a little while. When the tractor is already warmed up, like when I have shut it off for a few minutes, I just turn the key on and start it, the glow plugs go out when you let the key go back to the run posistion.

I don't think the glow plugs actually make contact with the piston, or that they would be hot enough to burn a hole in the piston.

 

[cmsedore]

Actually, in theory, it is harder on the engine to start it before the light goes off. The glow plugs (at least in the systems with which I'm familiar) heat for a fixed time (that is, they heat up until the light goes off)--so if you hit the key early, they glow plugs are colder rather than hotter.

The intent of the plugs is to provide a hot enough environment that the diesel will fire when compressed. If it is too cold, they barely fire, or won't at all.

In warm weather, it probably makes little difference. As it gets colder, I'd recommend waiting just to make it easier on the engine.

Just my $.02,

-Chris

 

[RoyJackson]

"I don't think the glow plugs actually make contact with the piston, or that they would be hot enough to burn a hole in the piston."

The glow plugs themselves aren't hot enough to burn a hole in a piston. However, the plugs in conjunction with normal combustion, may create a localized hot spot. Especially high compression engines such as diesels.
Normally, diesel pistons are thicker at the crown then those for gasoline engines and should take more pressures.
However, there is a reason the glow plugs cycle before starting, and don't continue to operate after the engine does start.
As I mentioned, I am making an assumption here...

Still kind of curious why they stay on as long as they do...although I've seen older Mercedes benz diesel glow plugs stay on for more then 30 seconds.

Let's see what the manual says. By the way, is this a new or used tractor?

 

[Ozarker]

Yes, it is bad for the glow plugs. The plug has an element that heats when voltage is passed through it. The purpose of that is to warm the combustion chamber. The length of time it is on has been determined by the manufacturer so that the chamber temperature rises to a specific temperature range to aid in ignition of the cold air/fuel mixture.

If the engine starts to run while the glow plug is still heating, the heat of ignition is added to the heat being produced by voltage flow. This MIGHT cause premature failure of the heating element in the glow plug.

It will not cause any damage to the engine other than possible excess wear on the starter becasue the chamber temperatire was too law causing more cranking revolutions before starting.

Let the glow plugs do what they were designed to do for the length of time they were designed to do it. That's why you bought the tractor to begin with wansn't it? To let the equipment do the work?

 

[Darren]

I doubt that the glow plugs will damage the pistons.Fuel burns evenly in a gas engine. In a diesel it explodes. Although it's an automotive application the glow plug controller in Navistar diesels in Ford trucks cycles the plugs on and off after starting to lower emissions immediately after the start.

Glow plugs draw enough current to dim the lights on a truck. I suspect the reason for not energizing the plugs during starting is the combined heavy current draws especially in the winter. Both at the same time may make it difficult for the starter to spin fast enough to start the engine.

 

[rozett]

G, I have the same tractor... if your glow plug light is really on for that long, you should have the dealer look for a bad plug. At this time of year, the light goes out in 10 seconds on my 7360. During the cold winter it might stay on 20-40 seconds. As has already been said, the issue is not damage, but making sure there is enough heat to ignite the fuel on initial compression. And that should not be a problem at this time of year..... except maybe yesterday when it was only 35 degrees. /w3tcompact/icons/smile.gif

 

[Alan L.]

On my Kubota B 2710, the glow plug is turned on just by turning the ignition key clockwise. Instructions are to hold in the intermediate position for 2 to 3 seconds then turn the rest of the way to start it. The light goes off immediately when you move on to the crank position.

 

[bgott]

Glow plugs don't heat the combustion chamber, they heat the pre- combustion chamber in an indirect injection engine. A direct injection engine doesn't have glow plugs, it has a heater to heat the intake manifold. The pre- combustion chamber engine, like an older Ford pick up with the 6.9 engine or the Mercedes diesel, is just about impossible to start with out heating the glow plugs. If the engine starts I wouldn't worry about it. You're not going to hurt the plugs or the engine.

 

[Kodiak]

In twenty two years the glow plugs in our old kubota L345 have had to be changed several times. There is no timer, you just hold the starter switch over till they are warm enough to fire that deisel fuel on the first revolution or two. If it doesn't fire then, repeat the process. As they get older they do take longer to heat up. They also build up a layer of carbon, that I suspect slows the heat radiating from them. Usually they blow a fuseable link or trip a circuit breaker in the glow plug circuit once they resistance gets to high for them to operate properly. And thats when I have replaced them.
Twenty two years, 1590 hours, changed glow plugs twice, just par for the course of her life.

 

[Ozarker]

........and the mixture in the pre-combustion chamber goes where?

http://www.freeautoadvice.com/diesel/glow.html

http://amghummer.com/Maintenance/DieselGlowplug.htm

http://www.ott.doe.gov/pdfs/jtb_diesel_engine.pdf

It's not a matter of your opinion or my opinion, it's a matter of physics. There is a reason you're supposed to wait for the light to go off:

1. Because the length of time the plug heats determines how high the air temperature gets and

2. Because the #1 cause of glow plug failure is over heating.

If you add the heat of ignition to the heat of the electrical current acting on the element, you will reduce the life of the element......period.

Use to have to replace the Cummins glow plugs in military 2 1/2 and 5 ton trucks regularly because young troops would hold the switch on a few seconds after the engine started. With current flowing through them and the engine running, they overheat.

 

[GlennT]

An observation somewhat off the track... I don't normally use the glowplugs on my JD 670 with indirect combustion chambers. The engine seems to start just as quickly and easily without using the glow plugs. Bear in mind that I'm using the tractor in south-central Texas with temperatures above 70 degrees. Even though the tractor doesn't seem to need the plugs, I've wondered if there are benefits to using them that I'm not aware of.

 

[Soundguy]

It is more likely that the resistance of the glow plug drops ( as it begins to fatigue and fail ), allowing more current to flow, thus allowing the breaker or fuse to pop, or allowing the glow plug to 'open'. Higher resistance will yeild lower current flow in a circuit, thus less heat at the element, and less of a chance a fuse or breaker will pop...

Soundguy

"Usually they blow a fuseable link or trip a circuit breaker in the glow plug circuit once they resistance gets to high for them to operate properly"

 

[GSS]

Mine seems to be the same. The light goes out when you turn it to the crank position, but the manual says nothing about 2-3 seconds. Just "wait until the light goes out"...

 

[GSS]

I'll start it a few more times and get a better feel for the time it takes to go out. They'll definitely be hearing from me if it's much different than yours. Thanks!

 

[RoyJackson]

"Even though the tractor doesn't seem to need the plugs, I've wondered if there are benefits to using them that I'm not aware of. "

Glenn, I've the same tractor you have. I use my glowplugs if the ambient temperature is less then 40°.
The sole purpose of them is to aid cold weather starting.

 

[GSS]

It's essentially new (ie warranty never activated), but it has 30 hours on it...

 

[bgott]

They were holding the switch for more than a few seconds then. Mercedes diesels leave the glow plugs on for 15 to 60 seconds after the light goes out, depending on model. Ford uses a post heat cycle on the Powerstroke. There are a few others also. Here is a link to a company that advertizes a two minute post heat. I've seen VW diesels that would take a month or two to burn the glow plugs out with the controller stuck and the glow plugs burning all the time. I doubt very seriously he'll burn out his glow plugs by starting the engine before the light is out.

http://www.beru.com/e/products/02/