Glow Plug Use

[JRH02]

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

I know there are at least a few decent YouTube videos. My problem with them is watching one 15-20m after another after another just to find out they didn't address their own title or so generally that nothing is gained. The days of a career in technical writing seems to be numbered in favor of wasted time behind a screen.

Last month I purchased a two camera and home base kit from Eufy and there is virtually no documentation except for stuff that is worthless because it covers so many models that are no specifics to any one of them. And their YouTube videos are equally worthless. I am still trying to tune the (outside) cameras to be usable for their intended purposes.

Just await for IRS publications to be only YouTube videos because people have lost the ability to read.

 

[aircommuter]

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?

Manuals aren’t what they used to be. In dealerships many basic learning is done with online orientation materials.

 

[JRH02]

OOPS - wrong forum

https://www.forbes.com/sites/zakdoffman/2026/01/11/kill-switch-iran-shuts-down-starlink-internet-for-first-time/

 

[dnw64]

I go for 20-30 seconds in idaho cold. Sometimes cycle 2 times. But this year I tested my glow plugs and only 1 of the 4 was working. I was noticing harder starts.

I replaced all 4 a few months back. Fires right up now.

Was 5°F yesterday, and only took 1 cycle of plugs

This. If it started fine in the past but not now my first suspicion would be defective glow plug(s).

 

[dkmc]

Manuals aren’t what they used to be. In dealerships many basic learning is done with online orientation materials.

Tractor manuals have NEVER been. I have the I&T and the OEM manual for my '57 IH 330 Utility. Both suck. Example: Section on removing the Torque Amplifier.......(I had to make tools to take it apart, and take the tractor farther apart to re-install it)....."Remove Torque Amplifier", To reinstall, reverse removal procedure".
Seems simple enough!

The engineers that designed farm tractors were quite creative. Probably still are.
Auto mechanics used to complain about working on Corvettes. Put them in front of
(or underneath) a farm tractor or forklift......HA!

 

[JRH02]

Tractor manuals have NEVER been. I have the I&T and the OEM manual for my '57 IH 330 Utility. Both suck. Example: Section on removing the Torque Amplifier.......(I had to make tools to take it apart, and take the tractor farther apart to re-install it)....."Remove Torque Amplifier", To reinstall, reverse removal procedure".
Seems simple enough!

The engineers that designed farm tractors were quite creative. Probably still are.
Auto mechanics used to complain about working on Corvettes. Put them in front of
(or underneath) a farm tractor or forklift......HA!

I have a BUNCH of 'special' tools in the shop AND in the house. While I somewhat agree with you, not everything is done to make servicing difficult.

 

[aircommuter]

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

The are ONLY useful when they are RED HOT.

Then of course let’s not forget the thermostart system which is also connected to fuel.

 

[aircommuter]

Tractor manuals have NEVER been. I have the I&T and the OEM manual for my '57 IH 330 Utility. Both suck. Example: Section on removing the Torque Amplifier.......(I had to make tools to take it apart, and take the tractor farther apart to re-install it)....."Remove Torque Amplifier", To reinstall, reverse removal procedure".
Seems simple enough!

The engineers that designed farm tractors were quite creative. Probably still are.
Auto mechanics used to complain about working on Corvettes. Put them in front of
(or underneath) a farm tractor or forklift......HA!

They’re not training manuals. Kinda like engineering plans for building the infrastructure on a subdivision. It’s not a plan for a carpenter or a mechanic. Certain amounts of knowledge or knowledge, experience and correlation are in order.

 

[Mike1955]

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!

View attachment 4673726

Har in your case, 23 years old I would imagine it would be a good idea to check out the entire glow plug system. That is ohm all four and make sure one has not gone bad. Because something has changed one the starting of the machine.

 

[JRH02]

They’re not training manuals. Kinda like engineering plans for building the infrastructure on a subdivision. It’s not a plan for a carpenter or a mechanic. Certain amounts of knowledge or knowledge, experience and correlation are in order.

The US Constitution was written so an average Joe could understand. There were no YouTube videos then. People could read.

 

[aircommuter]

Now we have states violating the Constitution even though it’s simple. Now it’s the vote seeking agenda.

 

[HAR]

I was chatting with my diesel mechanic friend yesterday, and he gave me a quick way to test if glow plugs are working. He said to disconnect the power strip from the glow plugs. Then, using a voltage test lamp with one end connected to the 12VDC power source, touch the other end of the lead to the post on the glow plug. If the light comes on, the plug is good. If not, the plug is bad. He said, glow plugs are like fuses. Either they allow power to flow or they don't. Such a simple test.

 

[aircommuter]

Continuity testing is always simple. However it doesn’t tell you if the plug opens with power.

 

[JRH02]

Continuity testing is always simple. However it doesn’t tell you if the plug opens with power.

This isn't very common for a glow plug, is it?

 

[grsthegreat]

I simply ohmed out my plugs, and found 3 open. Only one was working.

Biggest issue I had, my dealer gave me the wrong plugs. After I pulled the first one off…..I had to run back to the dealer. There’s a 1.5 hr peace of my life I’ll never get back. But the money saved by having me do the work more than made up for it. The dealer had a 7 day cycle to get repair done after I dropped it off. No thanks.

 

[aircommuter]

This isn't very common for a glow plug, is it?

I have seen a few. I have also seen some bulb filaments like that. One thing for sure if it tested open it’s done.

 

[HAR]

This diesel mechanic described the construction of the glow plugs and said that there were two coils inside. One sort of acts like a regulator and the other is the actual heating coil. He said, while the regulating coil might fail, it is primarily the heating coil itself that fails. He compared the coils to the old filament type incandescent light bulb...works fine, as long as it is a continuous strand. But if the strand breaks/melt/etc it is an open circuit and thus dead. While I suppose it might be possible for a broken/melted coil wire to have contact for a continuity check, I would be willing to bet that the odds are against that. He also pointed out, if you have to replace one plug, replace all plugs and do not mix brands/types/etc. Doing so is only asking for trouble. He also recommended OEM or OEM specified plugs.

 

[ponytug]

@HAR another vote to do what works for your engine.

I would comment that fuel also makes a difference, and trying to start on summer #2 diesel in the winter instead of diesel #1 will set most diesels back a bit. Add in a bit of gelation, and things are even harder.

I understand many newer diesel applications have auto preheat setups. I know the 2017 diesel truck that I use at my nephews maple sugar operation seems to have such a setup. Insert key, turn, and wait for all lights to extinguish before it will start. But it will fire and run right away, with no hesitation.

So, this brings up another question, which I think I knew about, but really have not followed. Engine warm up...some of these times seem pretty excessive, but what do I know. I do know that diesel engines are pretty cold blooded. What do others do?

View attachment 4673747

Due to the high compression in diesels, and the thermal expansion that happens as the engines warm up, yes most diesels do benefit from gentle treatment until they are thoroughly warm.
Can you use it before then? Sure.
Is it good for the longevity of the engine? Not in my opinion.
Might something else kill engine first? Yes.
It's your engine, but I would do what the manufacturer recommends unless I had a great reason.
Some engines are a lot better at cold starting than others in my experience.

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

The are ONLY useful when they are RED HOT.

Well, yes, but I would comment that not all "glow plugs" are in the engine, and even in the cylinder, some are a hot tip design and some have an exposed filament; some "glow plugs" are in the intake manifold where they preheat the air for more complete combustion, there are engine intake air preheaters on some Yanmars (and CATs), then you have the delightful thermostart systems on many older Yanmars that basically drip some diesel on a hot filament to ignite the diesel to heat the air intake. Vintage diesels came in hot bulb version where a protruding part of the combustion chamber had to be preheated with a blow torch before cranking.

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?

Having been around diesels, I would say that the manual is about par. So, yes glow plugs are pretty basic to diesel servicing, so I would expect a new trainee to at least know what they are, how they work, and how to check them. Most diesel mechanics probably have worked on a variety of engines, and glow plug control systems, and have a feel for the "lightbulb" nature of a glow plug. Get the ohm readings, if one or more isn't working, they all need replacing. Given the hassle of replacing most glow plugs, I do buy OEMs if possible, or at least from the company that made them for the OEM.

I've owned diesel engines that didn't care much about how cold it was if the battery was in good shape and the engine had a high output starter. I've owned others that you had to sit and wait for everything to get warm before they would catch and turn over happily. In my limited experience, some of the glow plug systems can put a sizeable load on the battery, and if the battery is weak (old, bad lot, sulfated, or just too cold itself) starting can be tough as then the starter isn't turning as fast as it should. There's a reason why there are batteries for northern states and batteries for southern states. The designs, additives, and details like the CCAs change.

I'm not a fan of starting a diesel on one cylinder as that stresses pretty much everything when it is least able to take it. If it doesn't fully catch for me at the start, I'll repeat the preheat cycle until it does.

Good luck on getting your Kubota sorted out.

All the best, Peter

 

[HAR]

I would comment that fuel also makes a difference, and trying to start on summer #2 diesel in the winter instead of diesel #1 will set most diesels back a bit. Add in a bit of gelation, and things are even harder.

ponytug:
You are correct in your comments about fuel grades. While I am not sure about the CA Bay Area, here in Vermont, and basically any state where temps consistently dip below 20F, winter mix fuel is and always has been a must. Our local fuel dealers automatically switch over before cold weather sets in. We also know it is okay to use up our winter grade up as weather warms, but do not go into winter with summer grade (straight #2) in the tanks. I even keep #1 (kero) handy to do some of my own 50/50 blend to use up my #2 prior to winter, before the dealer change over. And, once I have added any winter blend to my tractor tank, I run my engine long enough to ensure that the blend has purged through the lines and filter to the engine. At the same time, I remove and clean or change my fuel filter and purge any water that may have settled/collected over summer months. I made that mistake once! Not my favorite cold weather chore.

 

[ponytug]

They do switch summer/winter here as well, but for most folks it doesn't matter. We get some snow, so it matters a bit more for us, but nothing like your neck of the woods.

I did add intake heaters to my Deutz to help it out on cold days, mainly because the tractor doesn't have a clutch, so cold cranking involves moving cold oil through three hydraulic pumps at startup. The preheaters nothing for the cranking speed, but they do wonders for improving combustion, with no smoke on cold starts.

A cold soaked diesel has a lot against starting, cold air, low fuel temp, low block temperature (all work to reduce combustion), plus cold oil that adds to the load due to the tight tolerances, lower battery capacity, causing slower cranking...it all works against normal diesel function. I think that doing anything to help is usually rewarded.

All the best,

Peter