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  1. #1
    Elite Member
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    Mar 2009
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    Lee, IL
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    John Deere 1070

    Default glow plug question

    I understand that glow plugs are used to heat the combustion chamber for easier cold starting, what I don't understand is what are they actually heating? I have never had a head off a diesel to really see where they are oriented. Heating the air seems like a waste to me because after one crank that air is gone, and actually heating the head itself seems like it would take a lot more heat than what these could put out in that short amount of time. I am sure that this is a simple question to anyone that knows more about diesels than I do, so I apologize if this seems like a stupid question.

    I guess the reason I ask is because I don't notice much of a difference whether I use them or not. Maybe my glow plugs are no good? Would it be as simple to check them as just checking the resistance across the coil? I have never really had a hard time starting even around 10*F so I have never really worried too much about it. I am just curious I guess.

  2. #2
    Silver Member Little Red Tractor's Avatar
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    Apr 2012
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    129
    Location
    Gloversville NY
    Tractor
    Cub Cadet 6284

    Default Re: glow plug question

    If you post the tractor make and model, I'm sure one of the wizards here will tell you exactly how and where to test the glow plugs. If you see no difference, even at 10 degrees, be thankful! Not many of us have that luxury.

  3. #3
    Elite Member
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    Mar 2009
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    Lee, IL
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    John Deere 1070

    Default Re: glow plug question

    It's a jd 1070. I can't say for sure that there is NO difference as I have never done any scientific experiment with a stopwatch and thermometer. I just know that I was always using them anytime really below freezing, and on a few occasions, when quite cold- probably around 10, I thought "hey let's see if it starts without heating" and sure enough it fired up quickly. This has been attempted both with and without using the block heater. The bigger problem I have in the cold is sometimes the fuel solenoid stays stuck closed and I have to "help" it open a little, which is usually just a little push with the finger until it snaps open.

  4. #4
    Elite Member George2615's Avatar
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    Feb 2005
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    3,177
    Location
    Central Square, NY
    Tractor
    LS XR3037HC

    Default Re: glow plug question

    Not sure about your model but some tractors don't use glow plugs. Instead they use a pre heater in the air intake system. The object is to pre heat the combustion chamber (air fuel mixture) to a point that makes it easier to ignite under compression when cranking over. This is accomplished either with glow plugs, an intake air pre heater and in some cases a fuel heater. If any of these systems isn't working it makes it very hard to start in cold temps. A service manual (or maybe owners manual) should tell you what you have. The fuel solenoid problem should be fixed by replacing it.

  5. #5
    Elite Member Chilly807's Avatar
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    Sep 2009
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    Nova Scotia
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    Kubota L3400DT

    Default Re: glow plug question

    A typical setup is for the glow plug to extend into the pre-combustion chamber, not the actual combustion chamber. It creates a pocket of warm air for the fuel to ignite in as it's injected.

    Sean

  6. #6
    Gold Member
    Join Date
    Oct 2010
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    417
    Tractor
    08 Cub Ex3200

    Default Re: glow plug question

    Just heating the air like stated. Once the cylinder fires off that heat gets absorbed into the head and cylinder walls as well and eventually the cylinder will keep firing off. You may not notice it with such a small diesel. I've never had issues starting our tractor nor my duramax even in the coldest weather not using the glow plugs. Check out some cold start videos on youtube that feature diesels. Some times the engines only run on a few cylinders untill the others eventually light off enough to generate the heat needed to ignite the fuel being injected.

    Its seems the larger the volume of the cylinder the worse cold starting tends to be.

  7. #7
    Bronze Member
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    Apr 2012
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    kawkawlin,mi
    Tractor
    Rhino International

    Default Re: glow plug question

    My tractor has a glow plug on the air intake and when it is below 40 degrees it plain and simple will not start. ( after running battery dead and hooking up charger and using boost it sometimes will start). I put a in line heater in the bottom radiator hose and plug in 2 hours before I want to use it and problem is solved fires up on the first try.

  8. #8
    Elite Member Chilly807's Avatar
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    Nova Scotia
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    Kubota L3400DT

    Default Re: glow plug question

    Quote Originally Posted by dclynch View Post
    My tractor has a glow plug on the air intake and when it is below 40 degrees it plain and simple will not start. ( after running battery dead and hooking up charger and using boost it sometimes will start). I put a in line heater in the bottom radiator hose and plug in 2 hours before I want to use it and problem is solved fires up on the first try.
    Is the glow plug working? We used to have some older Perkins engines that were like that, often times warming the air in the intake with a propane torch got them lit off with no problems. Using the block heater is a great solution, easier on the engine too. But, for those mornings you forget to plug it in...

    Sean

  9. #9
    Veteran Member MHarryE's Avatar
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    Feb 2009
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    1,213
    Location
    Northeastern Minnesota
    Tractor
    JD 7720; Kubota M135GX, NH TS115A; JD 6230; Kubota L5740

    Default

    Most modern diesel glow plugs heat only the tip providing a hot spot, almost like a spark plug, to help ignite the charge. Heating the air in the combustion chamber is of little help because the first revolution pumps out all the air that was heated and draws in fresh, cold air. Google how glow plugs work, but ignore most of the answers until you get to a link to BERU. They are the premier maker of glow plugs and have good a good technical article on how glow plugs really work including cross sections of a glow plug, how the different types of glow plugs work(old ones stop heating after the engine begin to fire while new ones continue until the engine is firing properly). It also gives details on how to test without removing the glow plug.

    Like mentioned, older Perkins and some other engines heat the air in the manifold but the Perkins method used a coil plus fuel spray nozzle to ignite a fire in the manifold for heating. It only heated while the lift pump was supplying fuel but it did need to have a preheat for the fuel igniter coil to work. 2002 - 2007 Perkins engines (1.0 or 1.1 liter per cylinder sizes) used a computer to control - they would not open the valve unless the engine was turning over at 160 rpm or higher.

    Some answers say the glow plugs heat the combustion chamber. Think of how much heat would be needed to really heat all of that cold cast iron plus the coolant surrounding it. Now block heaters can do it. They are heating the coolant but the block heaters on our tractors are like 12 amps at 120 volts or 1600 watts and we usually heat for an hour on a cold morning. Now take a glow plug that draws 15 amps at 12 volts or 180 watts for 20 seconds for comparison - a fart in a windstorm. But it does create a hot spot - about 1,800 degrees F, that can light off a fuel charge down to about -30.
    JD7720; KubotaM135GX; NH TS115A; JD6230; KubotaL5740

  10. #10
    Elite Member
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    Lee, IL
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    John Deere 1070

    Default Re: glow plug question

    Thanks for the responses guys, and MHARRYE- I will check that out. I am always up for some more reading, I love new information. I am still curious whether my plugs are working or not, but as I said I have never had a problem so I haven't looked too much into it. Maybe I will just because the curiousity will get the better of me.

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