Should glow plugs be used when it’s warm?

The temperature is above 50 now, so I’ve just been starting my PD-TDI as if it were a gasoline car (no waiting for glow light). Is that acceptable?

It starts right up.

BeetlePD said:

The temperature is above 50 now, so I’ve just been starting my PD-TDI as if it were a gasoline car (no waiting for glow light). Is that acceptable?

It starts right up.

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That is because your plugs glow even if you don't wait for them. In warm weather, I don't bother to wait either. Just for your info it ain't gonna wreck your car. Motor on and don't sweat the details about trivial things unless you absolutely feel you need to post here to sleep well at night.

I’ve only driven my diesel 10,000 miles so far, so I’m still learning.

The ECU will determine how long the glowplugs need to be on, and yes, it may well turn them on some until the engine is warm to help with emissions compliance.


Personally, This is something I don't sweat about after winter starting is not a concern anymore.

Wait a minute. I'll ask my starter. My starter says yes please because at any temp, the pre-glow will make a cold engine start easier putting less stress on the starter.

BeetlePD said:

The temperature is above 50 now, so I’ve just been starting my PD-TDI as if it were a gasoline car (no waiting for glow light). Is that acceptable?

It starts right up.

Click to expand...

The short answer is that you're are not hurting anything. The long answer is a lot more complicated. The ECU controls the glow plugs and the time the GPs are actually on has nothing to do with the GP light on your dash. I'll explain.

By starting the car before the GP light goes out only means you shortened the pre-glow time. The ECU will keep the GPs on for a certain amount of time after the engine is running to get the combustion temperatures up to normal faster. That phase is called post-glow time. This post-glow time is for emission purposes.

I believe the ECU is looking at coolant temp to determine pre-glow time and determines post-glow time by measuring something else. What that something else is I'm not sure of because it varies by generation of engine.

Anyone familiar with GP mapping can add their comments.

Thanks. I had no idea there was post-glow time. When it was -10 in Minnesota those plugs must have been on for several minutes

Never ever heard of "post glow" time. Makes absolutely no sense.

VW did something many years ago on then newer model cars where the glowplugs came on when you unlocked the driver door and temperatures needed the glow plugs to come on.
They said the by the time your seat is in the drivers seat not much more glow plug time was needed.

Jetta_Pilot said:

Never ever heard of "post glow" time. Makes absolutely no sense.

VW did something many years ago on then newer model cars where the glowplugs came on when you unlocked the driver door and temperatures needed the glow plugs to come on.
They said the by the time your seat is in the drivers seat not much more glow plug time was needed.

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The door switch glow plug thing goes back to the pre-TDI IDI days. The pre-glow and post-glow thing started with the first gen TDIs in 1996, the 1Z, VW's first diesel that used an ECU.

Jetta_Pilot said:

Never ever heard of "post glow" time. Makes absolutely no sense.

VW did something many years ago on then newer model cars where the glowplugs came on when you unlocked the driver door and temperatures needed the glow plugs to come on.
They said the by the time your seat is in the drivers seat not much more glow plug time was needed.

Click to expand...

Post glow, or "afterglow", is used on all modern diesels. Has been for a long time. As Bk said, welcome to 1996 (for VAG anyway). It is to lessen idle emissions after a cold start. Also helps to keep the idle smoother when it is bitter cold for that first few minutes. MB does it. Ford does it. GM does it. Toyota does it. BMW does it. You get the picture...

The pre-TDI 1.9L diesel (which we never got in the US, but Canada did), did the preglow period trick with the door switch, same as the gas cars prime the fuel pump when you open the door. TDIs never did that, but the training literature still had that in there mistakingly, so the myth was started.

Even my 1991 Mercedes has afterglow. It makes the engine run smoother after starting, and reduces HC and PM emissions right after starting, too.

IIRC my 91 and 92 Jettas had afterglow as well.

The '91's afterglow is very short (a few seconds), and once it is done, it's done. No cycling on and off or any RPM input at all. And I would notice on SUPER COLD starts, that it would stumble a bit after the after glow period stopped. It would have been helpful to have it last maybe 15 seconds instead of 5 in some cases.

I noticed the same thing too... a longer afterglow would have helped on very cold days.

The short afterglow stumble helps me understand more of how my diesels have operated in colder weather. My neighbor, who was an OTR trucker, always said it was due to the colder fuel hitting the system, pumps, filter, injectors...

I get afterglow,after the engine starts.....

Jetta_Pilot said:

Never ever heard of "post glow" time. Makes absolutely no sense...

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Yes, unless you are hearing the EPA tells you what you will do in order to have your diesel engine certified for sale in the USofA.

Cheers,

PH

Alright, I stand corrected. This is the first I've ever heard of afterglow in 30 years of Diesel cars.

Jetta_Pilot said:

Alright, I stand corrected. This is the first I've ever heard of afterglow in 30 years of Diesel cars.

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Well, then you never needed to hear about it because it works well and has never been an issue that comprimised your car.

BeetlePD said:

The temperature is above 50 now, so I’ve just been starting my PD-TDI as if it were a gasoline car (no waiting for glow light). Is that acceptable?

It starts right up.

Click to expand...

For me, waiting for glow plug light to shut off is a very special ritual that I like to perform regardless of the weather - just because it is a diesel. And its a good habit to form for when the weather gets colder so that you don't kill your battery trying to start the engine without glowing first.

My answer is: No, it is not acceptable to diesel fanatics to not wait for the glow plug light to shut off every single time. Don't let us catch you "starting it as if it were a gasoline car".