Glow Plug Duration: Optimize for Performance

Hello everyone,

'Since I also use biofuel to run my engine, even during the winter and on these very cold days, it responds with a rather reluctant start, unless I run the pre-glow procedure, sometimes up to 10 times, depending on the outside temperature. After that, it starts surprisingly well, although it doesn't quite accept the throttle as eagerly for the first 20-30 seconds, and then after about 2-3 kilometers, it starts running properly.'

I now have the following questions:
- When I turn on the ignition, the glow plug indicator light goes out after a certain amount of time, but at the same moment, nothing is switched off (no click from any relay, and the blower motor speed doesn't increase). After a further period of time, a click can be heard from the area of the fuse box, and at the same time, the fan speed increases (indicating a load shedding). Why does the glow plug indicator light go out so much earlier?
- Is it possible to extend the preheating time, perhaps through the engine control unit? It would be great if we could avoid having to repeatedly turn the ignition key. There's also the option of installing additional electronics that extend the preheating time. Of course, a software solution would be the more elegant approach.

Hi,

The message only tells you how long the engine control unit (ECU) considers the pre-glow period necessary for a safe start (using diesel). After that, there's a brief "standby glow" period if you don't react immediately, and then it turns off. After the start, the afterglow period follows, lasting up to 4 minutes.

You can use an LED connected in parallel with the glow plug relay (usually relay 103) to observe its operation.

I would simply install two diodes and a switch in your place. With the switch, you can provide power to the glow relay in a way that you don't damage the outputs of the MSG (that's why the diodes). Then you can have the glow plugs active for as long as you like, and without much effort.

Best regards,

Jan.

Hi! While I can't answer everything specifically, here are some facts I've observed about my AKU (agricultural machinery) and RME (biodiesel) in extremely cold weather:

- The heating time is temperature-dependent (EDIT: This has nothing to do with RME).
- Below -10°C, preheating it multiple times can be beneficial.
- Preheating more than 3 times does not provide any significant further improvement.
- Give it a little gas when starting, because the idle fuel mixture might not be sufficient for the first few seconds. EDIT: So, in my case, the engine stalled for about 1 second after starting on one of the coldest mornings. The next time, I immediately gave it gas and was able to keep it running (at 1400 RPM).
Theory 1: It's possible that the idle speed control is not yet active during the increased cold start fuel enrichment, and a drop below the low-limit (LL) speed does not increase the fuel injection amount beyond the cold start enrichment, unless the accelerator pedal is pressed.
Theory 2: In the region of low engine speed (LL), the compression end temperature was so low, the atomization and combustion were so poor, and there was a regulator oscillation that, even with the maximum fuel injection amount, the engine could not run. When the accelerator pedal is pressed, the regulator oscillation is suppressed.
-When starting the engine from cold, apply consistent load (i.e., start driving immediately), shift gears early, and avoid high RPMs. This will help the engine reach operating temperature quickly and run smoothly.

Of course, this applies to a vehicle manufactured in 1998, and it certainly cannot be easily transferred to your car.

If necessary, you could try adding 10% Shell V-Power Diesel; it's supposed to ignite very easily. Make sure to mix it well.

Regards,
Holger.

Hello,
RME also has a good ignition tendency (cetane number), but its 'ignition temperature' is significantly higher than that of diesel.
As a result, it turns out that the preheating time for RME (Rapeseed Methyl Ester) specified by Volkswagen is too short; it should be longer than for conventional diesel.
Best regards,
Günther.

Hi Gunther, yes, the ignition temperature of that V-Power stuff is supposed to be extremely low, and the cetane number is 58.

However, the cold viscosity of the fuel also plays a role, as it affects the atomization quality. Very cold RME, in particular, can be quite viscous.

Considering that, in general, a fuel with a lower ignition temperature should also have a higher cetane number?

I would appreciate a well-explained explanation of the relationship between ignition temperature and cetane number.

Perhaps there are variables involved in the cetane number that are not relevant to the ignition temperature? For example, the ability to form highly reactive radicals under the atmospheric conditions that exist in the combustion chamber of a diesel engine just before the start of injection?

Regards,
Holger.

Hello Holger,
The flash point of RME is 170 degrees Celsius, and the cetane number is 56-58.
I once read that RME (biodiesel) absorbs a significant amount of heat (latent heat of vaporization?) during atomization, but I can't remember where I saw that.
'Definitely, the RME (residual methanol enrichment) requires a longer preheating time; therefore, my diesel engine starts poorly at 10 degrees Celsius compared to -10 degrees Celsius, even with three preheating cycles. At 0 degrees Celsius, preheating is not necessary.'
Best regards,
Günther.

Hello!

'Where exactly can I find this dual temperature sensor on a Volkswagen Golf 3 (1Z)?'
Can it also be tapped indoors, or only outdoors?
Control unit, i.e., located in the water tank?
(Would ideally also glow in the summer, in special cases.)

'How exactly does that work with the preheating relay?'
(Mine actually has 4 wicks in the burning chambers.)
and 3 units for the cooling water heating system; 2 of them are connected in parallel.
Then there should be 3 glow plug relays, but I only have...
'But I only found one, and it's located in the engine compartment.'
-> Do I also need to connect to that there?
(There are 4 x 20A flowing through it, it's that simple to cut off.)
It's probably not ideal to try and reassemble it.


Thank you for your responses!

Hello,
You can regulate this much more easily via the temperature sensor responsible for the preheating. This sensor is located in a plastic housing on the front left side of the engine, near the spark plug, in the G4, and is cooled by the coolant. You can now disconnect the connection cable and connect it to a switch inside the car. If the cable is disconnected, the engine control unit (ECU) receives a simulated temperature of -40°C, which allows for a maximum preheating time of approximately 20 seconds. I have elegantly solved this in my G4 using an original taxi switch that fits into the center console.
Sure, here's the translation:

"Hello"
Harald.

Hi.

Yes, I also had an idea for a "Force Glow" button.

I would interpret it as a button (or, electronically, as a timer). Because the temperature sensor is not only there for heating; it also influences all the processes that the engine electronics control.
And if it's not -40 degrees Celsius, the TDI engine starts acting up, especially with things like injection timing. I wouldn't recommend running it like that for extended periods.

The button should ideally be located on the left side, as the right hand is usually on the steering wheel (and curious passengers won't be able to reach it there).

m;

And where can I find the sensor on the G3?

I once read somewhere that you can change the preheating time in the engine control unit. I think it was adaptation channel 12 (no guarantee).

[EDIT] https://community.dieselschrauber.org/en/viewtopic.php?t=11122

@dieselmartin

There are several temperature sensors, and this one seems to be specifically responsible for the preheating process.
It can be easily done with a switch, and there are no issues, even with longer preheating times at higher temperatures. You can interrupt the preheating process by starting the engine whenever you want and then turn off the switch. However, even if you keep the switch pressed and fully utilize the afterglow time, there are no problems, based on my own experience.

@hollari
I don't know where the sensor is located on the G3. Just test them all: disconnect the connector, turn on the ignition, and see which one keeps the glow plug light on.

Sure, here's the translation:

"Hello"
Harald.

@hharry:

I've already unplugged countless plugs, but...
It doesn't need to be preheated.


Could it be possible that the G3 uses an NTC instead of a PTC?
That means I need to connect a specific resistance value?