Glow Plug Use

[Flogger]

My RTV 1140 is totally dependent on temps. From no glow plugs in warm weather to 15 seconds in sub zero temps.

 

[Jlillie2]

My tractor, which is not a kubota, turns the glo light off, when it is done. It usually takes around 30 seconds or so at the temps you are talking about, shorter if I've had it plugged in. Kubota, Yanmar and Bobcat equipment I have used do the same thing, you hold the key in position until the light goes off. Sometimes it might take 2-3 reps if it is cold and you don't have a block heater.

The B7300 glow plug is manual, its off is the operators hand. (Old school)

 

[Jlillie2]

Maybe this is an old topic, but I have searched, and while there is some glow plug discussion, I found nothing either serious or in depth.

When using glow plugs to preheat for cold starts, does anyone have any better information or knowledge about what is the proper/correct amount of time to preheat before trying to start a diesel engine?

The reason I ask is this. After having had my B7300 for over 23 years, I had my first cold start issue this past week. In the past, it seems, I really have not had the need to start my engine in really cold weather. However recently, we had a couple small snow storms, nothing enough to warrant clearing the yard and drive, but freezing rain was in the forecast, and following that a much colder freeze. I decided to clear up what was down and around before the rain and freezing rain made a mess, and the forecast deeper freeze turning everything into a rutted skating rink.

As it was about 15F at that time, I put everything in neutral, depressed the clutch, moved the key to preheat, and held it there for 10 seconds, basically what the manual said, and has worked in the past, but I cannot attest to what the temps were when I did those cold starts. However, this time, the engine did not fire on the first try. So, I waited about 1 minute, and repeated the process, and once again, it did not start. So, I repeated it for a third time, and the engine started. I did my clean up and put the tractor away, but I got to thinking about this, as winter here is basically just getting started. I reread my user manual, and confirmed what I had done was what was prescribed.

The next day it was much colder, 7F, and I decided to do a test. I went out and began the cold start procedure, but this time I held the key in the preheat position for 20 seconds, and it started right up. I am now wondering if the user manual is being a bit cautious with the preheat time? Or if maybe there is a more widely used or accepted thought/theory/procedure ?

BTW, Happy New Year 2026 to all!

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Yea, I found them to be a bit conservative. I generally do around 15 seconds in colder weather. (Or longer)
My dealer also told me that to help it along, you can hold it back on in the glow plug position for a few additional seconds after its running if it seems like its running rough.
(The B7300 is one of the few that can even do this as the key is not in the reverse ignition position like a lot of tractors are.)

 

[houdel]

If your manual says to cycle the glow plugs for only 10 seconds I would be very hesitant to cycle them for 20 seconds. My concern is if you leave them on for too long you could burn them out. In cold weather I cycle my NH glow plugs for 5 seconds or so, wait a couple of seconds and repeat. I also give it a little throttle when starting. If it chugs and smokes when it starts I give it another shot of glow plugs and it smooths out in a couple of seconds. Two or three 10 second shots is kinder to your glow plugs than a single 20 or 30 second shot.

You might have a bad glow plug as well. Check continuity to ground of your glow plugs. If you have continuity to ground they are probably good. If you don't have continuity to ground they are bad and should be replaced.

 

[aircommuter]

The challenge is measuring the temperature in the cylinders. All that ignition requires is one hot spot someplace in the chamber when the piston is at TDC. Usually, this will be someplace on the surface of the piston itself or the tip of the glow plug. Designing some sort of temperature sensor that would do something like turn on a non-sustaining indicator lamp is pretty much an impossible task. So the engineers and tech writers are left with recommending something that errs on the safe side. Once you have that first ignition, even if it only partially burns the fuel/air mixture, there will be plenty of heat on that piston head. More heat is going to result in better vaporization, which will reduce how much soot you belch on that first detonation, so they are going to recommend a longer preheat time than what is required to get it started, so as to reduce that puff of soot.

One problem is that we have too many sensors already. Too many problems.
Don’t forget pre-chamber systems

 

[HAR]

So, the glow plugs that I ordered arrived today. With them in hand, I took out my B7300 WSM (97897-12030), and what I did and did not find is amazing....little to nothing in it about them. Mind you, I had to thumb through the WSM page by page and literally almost read every page to find what I did find. Under the engine section, around the injector (Nozzle Holder Assembly and Glow Plug) section (pp 1-S19), it has two lines, basically "4. Remove the lead (4) from the glow plugs" and "5. Remove the glow plugs (1)". Just below, under "When reassembling", it does mention glow plug tightening torque (5.8-10.8 ft-lb). Then in the electrical system section, it has a small section labeled "Glow Plug" (pp 9-M5) sort of describing what glow plugs are for, and how they function, and that is it. A few pages later in the electrical system section, (pp9-S9) it has a part labeled "Pre-Heating" and basically has two short sections on testing the pre-heating system....1)testing power to the pre-heater power strip (should be equal to battery voltage) and 2) testing resistance in the glow plugs (approx. 0.9 ohms). And that is it. They spend more time explaining with photos and description on how to check and adjust the clutch pedal travel than they do with anything to do with how to remove, test, or replace glow plugs. As far as WSM's go, it was and is is pretty disappointing.

 

[CalG]

If your manual says to cycle the glow plugs for only 10 seconds I would be very hesitant to cycle them for 20 seconds. My concern is if you leave them on for too long you could burn them out. In cold weather I cycle my NH glow plugs for 5 seconds or so, wait a couple of seconds and repeat. I also give it a little throttle when starting. If it chugs and smokes when it starts I give it another shot of glow plugs and it smooths out in a couple of seconds. Two or three 10 second shots is kinder to your glow plugs than a single 20 or 30 second shot.

You might have a bad glow plug as well. Check continuity to ground of your glow plugs. If you have continuity to ground they are probably good. If you don't have continuity to ground they are bad and should be replaced.

I don't agree with much about "being kind to glow plugs"

The are ONLY useful when they are RED HOT.

 

[aircommuter]

So, the glow plugs that I ordered arrived today. With them in hand, I took out my B7300 WSM (97897-12030), and what I did and did not find is amazing....little to nothing in it about them. Mind you, I had to thumb through the WSM page by page and literally almost read every page to find what I did find. Under the engine section, around the injector (Nozzle Holder Assembly and Glow Plug) section (pp 1-S19), it has two lines, basically "4. Remove the lead (4) from the glow plugs" and "5. Remove the glow plugs (1)". Just below, under "When reassembling", it does mention glow plug tightening torque (5.8-10.8 ft-lb). Then in the electrical system section, it has a small section labeled "Glow Plug" (pp 9-M5) sort of describing what glow plugs are for, and how they function, and that is it. A few pages later in the electrical system section, (pp9-S9) it has a part labeled "Pre-Heating" and basically has two short sections on testing the pre-heating system....1)testing power to the pre-heater power strip (should be equal to battery voltage) and 2) testing resistance in the glow plugs (approx. 0.9 ohms). And that is it. They spend more time explaining with photos and description on how to check and adjust the clutch pedal travel than they do with anything to do with how to remove, test, or replace glow plugs. As far as WSM's go, it was and is is pretty disappointing.

They discourage self repair. Don’t you know.

 

[HAR]

Yeah, but this is from a Kubota WSM, which one would think Kubota would encourage a dealer to have and use. Unless, glow plugs are so universally used and recognized, that it is deemed unimportant to include?? But what of a new employee/apprentice/mechanic?

 

[Gregster613]

Yeah, but this is from a Kubota WSM, which one would think Kubota would encourage a dealer to have and use. Unless, glow plugs are so universally used and recognized, that it is deemed unimportant to include?? But what of a new employee/apprentice/mechanic?

Yeah - but go figure I guess! I learned more about glow plug removal techniques from u-tube than from any of my manuals!