Glow Plugs - What temp do they turn on?

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
At what temperature should the glow plugs stay on for a while? My 97 B4 is garaged, so I haven’t seen the early morning cold temps yet. But it has been in the low 40s or even high 30's more than once when I have left work for home and the car was parked outside. After turning the ignition on, the amber glow plug light has NEVER stayed on longer than ½ a second as long as I’ve had this car (6 momths). It always starts immediately, although it idles a little rough for a several seconds in cold weather and makes white smoke. But the white smoke always goes away shortly after I start driving it and it runs fine. Is this normal? In weather colder than the mid-40s with my Dodge truck with the Cummins diesel, the “wait to start” light stays on 20 seconds or more before it goes out.

So is this normal for the TDI, or do I have a glow plug problem? I don’t want to get left sitting with a TDI that won;t start when the weather dips into the 20s soon. Thanks for your feedback.
 

Joe_Meehan

Top Post Dawg
Joined
Sep 3, 2005
Location
Ohio USA
TDI
NB TDI, 2002.5, Silver
I believe they come on for a minimal time at every start. However I believe most if not all start extending the time at 40º F
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
Well, that is consistant with what I have seen. This is my first cold season with a TDI and is very different from my other diesel, so I wanted to be sure. Thanks for your feedback!
 

dieseljunkie

Veteran Member
Joined
Dec 29, 2006
Location
New England USA
TDI
96 Passat TDI wagon
I have a test light hooked up to the glow plug relay output so I can see exactly how long the glow plugs are on. The cluster glow plug LED duration has no correlation to the actual glow plug duration. At 40F to 30F the glow plugs are practically on for 3 to 4 minutes continuously but the glow LED for about 0.5 to 1 second. Glow plugs are on continuously for the 3 to 4 minutes except when I shift and the rpm goes above 2500 RPM where the glow plugs go off for that split second and comes back on immediately and stay on for the 3 to 4 minutes till the coolant warms. I'd be curious if your's do the same. The test light is easy to make and hook up. Wrap one end of the test light wire to the glow plug relay big terminal and plug it back in and the other end of the test light wire to ground.

PS. From what I read, glow plugs do not come on above 40F. I have seen mine go on at 50F for a short time. Not sure if there is something wrong with my temp sensor.
 

Joester

Vendor
Joined
Aug 17, 2009
Location
St. Louis
TDI
2002 Golf TDI
frst time it was freezing out my GP light (02 A4 ALH) stayed on for about 5 secs. ive heard 40 F was the degrees too.

oh and mine kinda stutters and runs rough for about 3 seconds and then it clears up.
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H
The white smoke is a sign that the glow plugs are not working as intended. The white smoke is unburned fuel. No time on the indicator (other than the lamp check) at 40F is about where I'd start to be suspicious that the circuit isn't working. 40F is about where they pre-start glow phase would begin to be introduced. Definitely by 35F.
The glow plugs are on (before starting) for about three times the duration of the indicator lamp. Lamp for 10 seconds? Pre-start glow for about 30 seconds. Think of the lamp as a minimum suggested wait time before cranking.
Once started the glow plugs turn back on until the coolant is up to some temperature (90F?) or the RPM exceeds 2500. When the temp AND rpm are both low the glow plugs are on. This post start glow phase is not time dependent, but is temperature and rpm dependent. This post start glow phase will occur even if the pre-start glow phase isn't used. Start your car in the summer at 80F and you'll have post start glow plug operation. There is no indication from the cluster for the post start glow phase.

Here's a quick check: unplug the electrical connection at the temperature sensor in the upper coolant hose. Turn the key to ON and see if the glow plug indicator stays on for longer, about 20~30 seconds. Then start the car to see if the white smoke is not produced.
As DJ pointed out above, the indicator is not directly tied to the glow plug power, but is somewhat independent. Just because the lamp is on, or is off, does not indicate for sure that the glow plugs are being powered, or not.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
So much (mis) information here, some good some bad. :p

First, the TDI's glow system operates at every start from ambient temps on any day of the year in any state or province in North America. Yes, you read that correctly. Your car sat overnight in August in Florida, guess what? When you start your car up, the plugs get powered up.

Now, for how long (both for the pre-glow and post-glow) depends on coolant temp and RPM.

The indicator in the cluster is NOT an indicator of whether or not the plugs are powered up, but an indicator of when the system says you can start the engine. The plugs may remain powered up, under 2500 RPM, for several minutes... longer periods in the cold. This is normal. This is called afterglow, post glow, or whatever, and is intended mainly for smooth running and lower emissions during warm up. Older (pre-TDI) VAG diesels did not do this. Their post glow was about 3 seconds, and once the relay clicked off, it stayed off.

Pre-2002 TDIs have their glow plug relay in the inside of the car, in the relay box, and it is normal to hear it clicking on and off as the car warms up. Every time you sweep over 2500 RPMs, it clicks off. Then back on again when it sweeps below 2500 RPMs. It will do this until the coolant is up to a temp predetermined by the ECU's programming that says "OK, the engine is warm enough, we can keep the plugs off". 2002+ cars placed the relay outside the car, near the ECU (on Golf/Jetta/NB) and under the coolant bottle (on Passats) and they are actually a slightly different functioning relay (duty cycled) but that is not important right now.

If you feel your preglow period is somewhat short, meaning the time the light stays lit, you *may* have a faulty coolant temp sensor that is not giving the correct value to the ECU. So, if it is 25 F out, and your ECU is getting a signal that it is 75 F, the preglow will be shorter than ideal. But since 70 F is within the normal range of the CTS, the ECU will not flag this as a fault.

While you can electronically lengthen the preglow period with VCDS or similar on many cars, keep in mind these items:

1: some light smoke on a cold start and during warm up is normal It is even stated in the owner's manual.

2: improper timing of the pump, a worn pump, poor injector spray pattern, poor fuel, weak compression, etc. can also cause some excessive whitish smoke after a cold start.

3: a weak battery can also cause excessive smoking, as not only will the engine not crank as fast as it should, the glow system will be placing a massive drain on it both before and after the starter has done its job, further increasing smoke as the electricity to the plugs is reduced and they won't get as hot as quickly.

I have started countless TDIs up cold, have owned them from new all the way to nearly 400k miles, VEs and PDs, and they should all start right up down to single digit (F) temps without too much drama. However, they are all going to put some puff of something out the tailpipe. It may not be enough to see every time, but standing behind the car you'll see something and again, this is normal.
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
First of all - thank you to EVERYONE for their replies. I feel better about what my car is doing after reading everything.

To comment of Oilhammer's notes:
1: some light smoke on a cold start and during warm up is normal It is even stated in the owner's manual. I would characterize my white smoke on cold startup as "light". It is only there at cold startup, does not "billow white clouds" out of the tailpipe, and quickly disappears.

2: improper timing of the pump, a worn pump, poor injector spray pattern, poor fuel, weak compression, etc. can also cause some excessive whitish smoke after a cold start. I can't speak of the condition of the injector pump, but compression was checked and deemed "within specs" by a competent VW shop on the TDI friendly mechanics list here when I bought it 8000 miles ago. They also adjusted the timing with VAGCOM when I had them replace the TB immediately after my purchase of the car. The injector nozzles are 190K miles old, but I have new Sprint 520 nozzles and a RC2 tune going in there within the next 2 weeks.

3: a weak battery can also cause excessive smoking, as not only will the engine not crank as fast as it should, the glow system will be placing a massive drain on it both before and after the starter has done its job, further increasing smoke as the electricity to the plugs is reduced and they won't get as hot as quickly. The battery was load tested just 1 month ago. I was not happy with the cranking speed, so the afore-mentioned shop installed a Bosch starter relay kit. It now turns over VERY quickly and the motor starts in less than 1/2 a second in any temps experienced so far (mid to high 30s). In colder weather, it idles a little roughly for 3 or 4 seconds and then smooths out. It drives normally even when stone cold, although I try to keep the revs down until it warms up.

Thanks again for the feedback. Y'all have been a great deal of help.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Sounds to me like your car is behaving pretty normally. Keep in mind, every time you start the car from ambient, the ECU runs a test of the glow system. If there is an issue, it will store a fault (DTC) and illuminate the check engine light (MIL).

So there really is no need to test your glow system.
 

dieseljunkie

Veteran Member
Joined
Dec 29, 2006
Location
New England USA
TDI
96 Passat TDI wagon
oilhammer said:
Sounds to me like your car is behaving pretty normally. Keep in mind, every time you start the car from ambient, the ECU runs a test of the glow system. If there is an issue, it will store a fault (DTC) and illuminate the check engine light (MIL).

So there really is no need to test your glow system.
Is this true for my 96 Passat? I thought I've read on this forum that the 96 BK ECU does not perform diagnostics on the glow plug system.

Quote: "So much (mis) information here, some good some bad. :p "

Sorry I did not make this clear but I was posting about how my glow plugs operate to get feedback on whether it is operating normally. If you see any mis-information, please point it out.
 
Last edited:

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
'96 B4 does not have the same glow plug monitor system, that is correct. The OP listed a 1997 model, which does.

I will yield to Lug Nut's greater learned knowledge of the 1996's differences, as almost every one I ever see anymore has the newer 1997 ECU installed. And there are not too many 1996 models that come through my shop any more anyways.:(
 

dieseljunkie

Veteran Member
Joined
Dec 29, 2006
Location
New England USA
TDI
96 Passat TDI wagon
Why does my TDI engine have a second or so of white smoke (colder it is, more and longer smoke) but my IDI's does not smoke at the same ambient?
 

bmike

Thread Killer
Joined
Jan 3, 2002
Location
central CT
TDI
1998 Jetta - sold, 2010 A3 - sold
LeadSSled said:
I was not happy with the cranking speed, so the afore-mentioned shop installed a Bosch starter relay kit.
What is that?
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
bmike said:
What is that?
The VW shop recommended it when I complained about the cranking RPM. They said that it is a kit that Bosch makes that adds a relay to the starter circuit to reduce the voltage drop. It is described as a "starter relay kit" on my invoice at $34.22 for parts with 1/2 hour of labor ($40) to install it. The motor turns over nearly twice as fast as it did before the kit was installed. To me it was well worth the less than $75 installed cost. My motor always fires up almost instantaneously now.
 

mike944

Veteran Member
Joined
Aug 18, 2004
Location
Vernon, Ct
TDI
2004 Jetta
If you don't like the glow time, you can adjust with vag-com. Search around here for the instructions. You can't directly set the time, but you can turn up the temperature where the system first activates, so it effectively lengthens the time at the lower temperatures too.

let me elaborate a little on what oilhammer said, to make it a little clearer. Yes, the system runs every time you start the car for a few minutes, but it's only AFTER you start the car. (known as post-glow)

When most of us think of "glow plugs coming on" it's after we turn the key, but BEFORE we start the engine. (known as pre-glow) In the VW, that doesn't normally happen above something like 35-45F. Which is unusually low for a diesel. Fortunately, you can adjust.

I have mine set pretty long (high temperature). IMO it starts much, much easier now.

Check your temperature sensor first.


I may look into that start relay thing. mine cranks kind of slow for my liking, and my battery is only like 1yr old, and connections are all clean. Do you know any more about this starter relay kit? Does it bypass the electrical portion of the starter solenoid? Can you get a part number off of it?
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
mike944 said:
I may look into that start relay thing. mine cranks kind of slow for my liking, and my battery is only like 1yr old, and connections are all clean. Do you know any more about this starter relay kit? Does it bypass the electrical portion of the starter solenoid? Can you get a part number off of it?
I'll talk to the guy at the shop that did it in the next couple of days and will ask for more information. I need to schedule a stop in there anyway. When I have details, I'll post back here. It made a big difference with my car.
 

Lug_Nut

TDIClub Enthusiast, Pre-Forum Veteran Member
Joined
Jun 20, 1998
Location
Sterling, Massachusetts. USA
TDI
idi: 1988 Bolens DGT1700H
Joe_Meehan said:
Or just moisture.
Without a volume or size description of the cloud, it very well could be normal steam condensation.
The description given in post #1 fits something other than typical cold weather condensation.
it idles a little rough for a several seconds in cold weather and makes white smoke. But the white smoke always goes away shortly after I start driving it and it runs fine.
When that (white smoke, rough idle, followed by no smoke and smooth idle) is combined with the comment about a perceived brevity of glow operation I was led to the glow plugs as a more likely cause.
Steam wouldn't cause a rough idle.

The 97 checks glow plugs as paired sets. Only a resistance difference between the pairs will be identified as a fault. If TWO glow plugs are inoperable, and they are each on one of the two circuits, then the circuits will still be 'balanced', no fault will be produced.
There will still be a rough idle and copious amounts of atomized, unburned diesel diesel mist.
A long lasting large cloud with a distinctive diesel odor is different than a short lived, quickly dissipating, thus small in size, condensation trail.
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
I was in there yesterday and my middle-aged brain forgot all about it. I just shot him an e-mail though and will respond back when he returns my message (if I remember ;) ).
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
mike944 said:
Hey LeadSSled - did you ever find out more info about the starter relay kit?
OK, here is the good word. It is a WR1 Bosch Starter Relay kit. If you can't find one, I can buy it from him for $35.52 including sales tax and could ship it to you.
 

BolaB4V

Veteran Member
Joined
Dec 30, 2007
Location
Northern NY
TDI
1996 passat tdi wagon, 97 F-150 XLT 4x4, 99.5 Mk4 Jetta VR6/5M
It was around 2 degrees fahrenheit (not counting wind chill factor) here today. My 96 passat started very hard, but started after 3 tries.

Just read in another post that; if you turn on key and crank engine over a couple times before cylcling the GP's it primes the fuel pump or some such thing. Then cylcle GP's as usual and it will start better/easier.
Wonder if thats true?
 

mike944

Veteran Member
Joined
Aug 18, 2004
Location
Vernon, Ct
TDI
2004 Jetta
Thanks for the info on the starter relay. I searched, and i can find them lots of places. Plus, i found some info on how the work. It basically takes the lead from the keyswitch to the starter solenoid, and puts a relay in-line. So the key runs the relay, and the relay runs the starter solenoid, and the starter solenoid runs the starter motor.

The kit looks like it was designed to solve a hot-start problem. I'm not sure i understand how that helps the starter crank better at low temperatures, but i guess i can give it a shot. It's just a relay. i have the parts lying around to make one from scratch. If i can figure out a way to try it out without permanently modifying anything, i'll give it a shot. otherwise, i'm kind of skeptical about it.
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
Yes, it basically makes the wiring through the switch a control cicruit for the relay. All I can tell you is that it helped my slow cranking issue when cold. Good luck.
 

LeadSSled

Veteran Member
Joined
May 21, 2009
Location
Knoxville, TN
TDI
97 B4 Passat TDI
LeadSSled said:
It always starts immediately, although it idles a little rough for a several seconds in cold weather and makes white smoke. But the white smoke always goes away shortly after I start driving it and it runs fine.
FWIW I had the 190k-mile stock inejctor nozzles replaced with Sprint 520s last Tuesday. The startup white smoke in cold weather is now significantly reduced, and it idles much more smoothly too! So I'm concluding that worn injectors can contribute to the cold-start smoke.
 

bbaughman2008

Member
Joined
Apr 22, 2015
Location
south carolina
TDI
99 beetle
2000 tdi 1.9

i need some help plz. My daughters was starting ok. Only at random times do I ever see the glow plug indicator come on at the dash. I have several questions.
1) does the fuel sender sending unit in the tank help the fuel system hold prime or help keep pressure on the system until the injector pump starts pumping again when ever the car is started.
2) my car isn't starting at all now unless I bleed the fuel system and then I don't see the glow plug indicator. So does it not always need glow plugs to start. Need a direction to start
 

Steve Addy

Top Post Dawg
Joined
Aug 7, 2002
Location
Iowa
TDI
97 Mk3
i need some help plz. My daughters was starting ok. Only at random times do I ever see the glow plug indicator come on at the dash. I have several questions.
1) does the fuel sender sending unit in the tank help the fuel system hold prime or help keep pressure on the system until the injector pump starts pumping again when ever the car is started.
2) my car isn't starting at all now unless I bleed the fuel system and then I don't see the glow plug indicator. So does it not always need glow plugs to start. Need a direction to start
There are two one-way valves in the fuel lines that keep the fuel from going backwards through the system, ie should keep the supply side full at all times.

If you're having to bleed the system every time then you have some sort of leak on the supply line. Do you see air bubbles in the translucent portion of the supply line? I would look there to see if air is getting in somehow. The system must be completely sealed in order for the lift pump to work properly.

The T fitting at the fuel filter, or really the T fitting o-ring, is a known weak point. You might be getting air into the system from a bad o-ring.

As for glow plugs, they don't come on above 40 although the dash indicator should appear briefly when you turn the key to the on position prior to starting.

If the GP system is working right you will always see the light at startup even if the temps are such that they aren't needed.

Steve
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
If there is no glow plug light at key-on, you probably have a relay 209 problem.
 
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