Glow plug light, to wait or not to wait

[Crankytank]

I have noticed that my engine starts the easiest, just after the glow plug light goes out. If I wait any longer to start the engine after the glow plug light goes out, then the engine takes longer to start. It's as if the glow plug continues heating after the light goes out and makes it too hot and hence harder to start the longer you wait.

Should you always wait for the glow plug light to turn off before starting even when engine is hot.
After the light goes out do the glow plugs continue heating.
Do the glow plugs not even operate unless the engines computer tells them too. Eg. if the engine is hot the plugs may not come on.
When engine is hot is it best to wait for the glow plug light to go out anyway, because the plugs are using battery power and if you crank while they are on, then its too much current for the battery and not good for battery life etc.

 

[Whizbanger]

On my F350, the colder the engine, the longer the light stays on. If I were to take a guess, the truck takes engine temp into account when setting the light.

 

[expat]

I only ever use the glow plug feature on a cold start. Even then I will often start befor the light is out.

I guess I'm just impatient.

 

[supton]

I'm guessing we don't have whatever motor it is here in North America, but it might be nice to indicate what it is on. Just in case it matters.

On my TDi, no issues. Crank with the light on or off. If I don't wait it will just smoke a bit. And sometimes not. But it won't trigger a check engine light.

But on mine, if it is a hot engine, the light stays on very briefly if at all.

No idea on cranking. But I'd suspect that the glowplugs stay on during cranking--last thing you want is for the plugs to cool off while trying to start it. Again, for my TDi, I think it draws maybe 50A (or it's a 50A fuse, don't remember now). As compared to ??? amps for the starter.

Finally, my glowplugs may stay on while the engine is running, for many minutes. I've never checked but have read where others have, and have noticed that they stay on. Well, "on" but at a lower power level. On my car they use PWM to modulate the effective voltage, and as such they can leave them on but at a low power level. Just to make sure things stay good and warm.

 

[Shannow]

Glow plug starts cooling after the light goes out typically...not always.

If you are experiencing harder starting after the light goes out, then that's likely (IMO).

My Navara (still don't know what you are driving) apparently runs the plugs for 5 or so minutes after a start, which means that my Mrs driving around town uses them up badly.

 

[Astro14]

Originally Posted By: Shannow
Glow plug starts cooling after the light goes out typically...not always.

If you are experiencing harder starting after the light goes out, then that's likely (IMO).

My Navara (still don't know what you are driving) apparently runs the plugs for 5 or so minutes after a start, which means that my Mrs driving around town uses them up badly.


Yep...this...

Takes heat to ignite the fuel (heat of compression, when the engine is warm...glow plugs when it's cold) and the plugs are cooling as soon as the light is goes out...

 

[morepwr]

On my Duramax I usually wait for the light when I start it first for that day. Once the engine has any warmth, the light doesn't even come on when I restart it. If I don't wait for the light to go out when I start it, it still starts just as easy but it doesn't really get cold where I live.

 

[bullwinkle]

Usually when you hear the "click" of the GP relay, that's the time to crank. Usually that's when the light goes out, but there are exceptions (the MB in my sig). Imagine an incandescent light bulb when you turn it off-cools off pretty quickly.

 

[bullwinkle]

Also most newer GP systems are temperature compensated-like my Ram Cummins which doesn't even show a light above 80F.

 

[Chris142]

im sure that the glow plugs turn off when the light goes out and begins to cool imediatly. it cant be too hot to ignite the fuel but the glow plugs can burn out and swell if left on too long

 

[artificialist]

I have no way of knowing exactly how your glow plug system works unless you have a purely mechanical diesel, or a computer controlled diesel. A mechanical diesel may simply use a timer to decide how long to light the glow plugs, whereas a late model mechanical diesel or electronically controlled diesel may base glow plug time on ambient temperature and/or engine coolant temperature.

If you have a huge technician's manual for your vehicle, it may tell you how the engine determines glow plug lighting time.

There are other reasons different diesels have different glow plug times. Old toaster style glow plugs needed more time than more modern ceramic-tipped plugs. Mechanical diesels sometimes need more time to start than computerized ones. Having a prechamber or direct injection is another big factor.

Sometimes people need extra help starting their engine in extreme cold. They may turn the key to the on position, wait for the plugs to cycle, do that again, and then start their engine.

 

[Lyman]

Been a truck driver for 30+ years. I only ever wait for the glow plug on cold starts. And then crank it right after it goes out.

 

[Silk]

The glowplugs have afterglow - sometimes they pulse, sometimes they get reduced voltage. The glowplug timer gets a reading from the coolant temp sensor and gives the appropriate amount of glow. After market glowplug timers don't take the coolant temp sensor into account...but you can adjust glow and afterglow separately. I'll assume it's a Japanese diesel seeing as you are in OZ.

 

[Fleetmon]

Our BMW "decides" when to start....when it's below 15'F or so in the garage and you push the start button, occasionally there's a short delay before the starter engages and we get the glow plug symbol on the dash....We've only had the glow plug symbol/delayed start a handfull of times since we've owned it.