2008 BX 2350 Glow Plugs Indicator Stays on After Starting Engine

[Eagle1]

I would assume battery voltage at the buss bar when preheat and nothing (near nothing?) when not heating.

 

[GrandpaSmurf825]

It sounds like without being able to troubleshoot it that the relay probably has the contacts welded shut on it. The relay is going to be energized when you go to start or heat. If the contacts stick it will heat the glow plugs as long as the key switch is in the on position. It appears as though its just a Bosch style automotive relay but it might be higher amperage or something proprietary. You can unplug it and test as the manual states on page 440. If it has welded the contacts it will show continuity 2 and 3. The way they state it in the manual is confusing. That's the important part to check. If that doesn't show they are welded then you probably have a more serious issue. This is definitely where I would start though.

 

[GrandpaSmurf825]

Okay. So my plan to start will be to test the voltage and see if the glow plugs are actually being energized. Can anyone tell me what the voltage should read on a multimeter when the glow plugs are in the preheat mode versus what they should read when the tractor is in operation? I assume I should be testing the voltage on the hot lead that you pointed out, number two

Page 448 says you should be seeing battery voltage at the glow plugs. See my earlier post about checking the glow plug relay. It isn't uncommon for relay contacts to get welded. Also check your battery voltage. It doesn't have to drop much to cause amperage to increase to levels that can cause damage. It is often overlooked because if it starts it has to be good right? Generally that's true unless it takes some extended cranking.

 

[rScotty]

Page 448 says you should be seeing battery voltage at the glow plugs. See my earlier post about checking the glow plug relay. It isn't uncommon for relay contacts to get welded. Also check your battery voltage. It doesn't have to drop much to cause amperage to increase to levels that can cause damage. It is often overlooked because if it starts it has to be good right? Generally that's true unless it takes some extended cranking.

It would be a good pencil and paper exercise to run some sample voltages in Ohm's law and watch what happens to the amperage.
I just don't see how a voltage drop can cause amperage to increase. Can you give any examples or explanation?
Thanks,
rScotty

 

[Hoho223]

BobCat CT120. Mines does that also but intermittently. It is a cold weather event. Don’t remember it happening in the summer.

 

[GrandpaSmurf825]

It would be a good pencil and paper exercise to run some sample voltages in Ohm's law and watch what happens to the amperage.
I just don't see how a voltage drop can cause amperage to increase. Can you give any examples or explanation?
Thanks,
rScotty

It's the same as the same motor wired for 240 draws half the amperage as it does on 120 volts.

Ohm's Law

If voltage decreases and resistance is constant, current increases

 

[rScotty]

It's the same as the same motor wired for 240 draws half the amperage as it does on 120 volts.

Ohm's Law

If voltage decreases and resistance is constant, current increases

No, that's not right. Voltage and Amerage are proportional. If resistance is constant, then when voltage goes up or down the amperage follows. More voltage causes more amperage to flow, and vice versa.

And your sentence is not correct for Ohm's Law. Look it up anywhere. The sentence should say that if voltage decreases and resistance is constant, current decreases as well. Solve some examples and you can prove it to yourself. Ohm's law says amperage equals voltage divided by resistance.

I think the confusion comes about because a motor is not a very good example of pure resistace, and so using a motor makes it easy to confuse wattage with Ohm's law. Wattage is power, which is not the same as electrical resistance.
Wattage does equal voltage times amperage, so when power is held constant and you double the voltage then you can produce the same power at half the amperage. Hence the confusion.

What happens when you double the voltage to a motor with no load on it is that the coils will pull twice the amperage and the added force will try to run the motor at twice the speed. In a perfect frictionless vacuum that is what would happen for as long as the coils can handle the heat.

But if you put a load on a motor and only let that motor rev up to meet the load, then you are right that doubling the voltage will create the same power at a lower amperage.

In a glow plug there is no limit to the load, so decreasing the voltage will simply decrease the voltage and the glow plug will not get very hot.

Hope this helps,
rScotty

 

[GrandpaSmurf825]

No, that's not right. Voltage and Amerage are proportional. If resistance is constant, then when voltage goes up or down the amperage follows. More voltage causes more amperage to flow, and vice versa.

And your sentence is not correct for Ohm's Law. Look it up anywhere. The sentence should say that if voltage decreases and resistance is constant, current decreases as well. Solve some examples and you can prove it to yourself. Ohm's law says amperage equals voltage divided by resistance.

I think the confusion comes about because a motor is not a very good example of pure resistace, and so using a motor makes it easy to confuse wattage with Ohm's law. Wattage is power, which is not the same as electrical resistance.
Wattage does equal voltage times amperage, so when power is held constant and you double the voltage then you can produce the same power at half the amperage. Hence the confusion.

What happens when you double the voltage to a motor with no load on it is that the coils will pull twice the amperage and the added force will try to run the motor at twice the speed. In a perfect frictionless vacuum that is what would happen for as long as the coils can handle the heat.

But if you put a load on a motor and only let that motor rev up to meet the load, then you are right that doubling the voltage will create the same power at a lower amperage.

In a glow plug there is no limit to the load, so decreasing the voltage will simply decrease the voltage and the glow plug will not get very hot.

Hope this helps,
rScotty

You are correct. I definitely got that one wrong. Thank you for correcting me. After digging into it more I agree that the amperage should drop as the voltage drops. Sometimes as they say it's better to let them think you are an idiot than to open your mouth and erase all doubt. Or something like that.

I do know that low voltage damages starters. Whether this is due to high amperage I can't say. We used hundreds of starters and alternators a year on our equipment. We had a local commercial rebuilder who worked with us directly. More than once when I picked up a starter he advised to check our charging system and batteries because the starter showed damage from low voltage. Take it for what it's worth but there is wisdom from hands on experience in those words. (Sadly they had no one to take the business over and they closed last year because they were up there in years. Like many of us) More often than not the starter had failed when we took it in but the root cause could have been driven by voltage issues and not just normal wear and tear. Yes starters can of course be burnt up by excessive cranking without cool down time as well. I've saw a few smoking starters in my day.

 

[fustsgt]

Sounds like you have to turn the ignitions switch back to ON. My Ford ignition switch is the same way. There's four positions: Off, On, Glow, Start. If you turn the key to Start then just release it, the switch returns to Glow. You have to physically turn the key back one position to On.

That sounds counter intuitive. Why relax from start to glow? Glow is a spring loaded return to off on my Shibaura. Glow-off--run-start

 

[fustsgt]

It would be a good pencil and paper exercise to run some sample voltages in Ohm's law and watch what happens to the amperage.
I just don't see how a voltage drop can cause amperage to increase. Can you give any examples or explanation?
Thanks,
rScotty

A some what common fallacy, probably derived from motors...in order for the motor to deliver rated horsepower, when voltage goes down, current has to go up.