I just purchased a wonderful E-class 300D from Texas. I have a small question which has been on my mind. Again, I'm new to Mercedes and diesel engines.

The glow plug light does not come on when I wait to start the engine. If it does come on, It's after the car starts, and is on for 45 sec.

Do I need a new glow plug? Is it working correctly?

The later model diesels had a very fast acting glow plug system, so it would not surprise me if, in the summertime, the glow plug light didn't come on when turning on the ignition. But coming on after 45 seconds is not right.

I doubt that the glow plugs(there is one for each cylinder) are the culprit here. If the light is coming on under these conditions, the problem is probably relay or wiring related.

Good luck,

The glow plug light on our '96 E300 Diesel will come on each time, even if the engine has just been off for a few minutes.

I'd vote relay or wiring gremlins.

BCingU, Jim

JIM H,
Does your Wife's car actually have 735K???
WOW!!

And here I was smug in thinking that my 240D has been a long lasting vehicle!

Have a great day,

When you say the light comes on, is it flashing or on steady? I recently had my glowplug light flash after the engine was running. It turned out to be a loose wire on the #1 glowplug. I don't know if the newer glowplug systems had this diagnostic feature.

__________________
1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

Maybe I'm not the brightest glow plug of the bunch, but because I'm new to MB and Diesels I will try to explain what is going on again with better detail.


I can get the glow plug light to come on if I wait 1 min. or 2. The light is steady.... If I wait for it to go out It seems to take 2-4 min.

Is this normal? I start the car (if it's warm) right away and the plug will come on after it starts. Then it go's out after about 45 seconds or so.

Do I need new Plugs?
Or do I need the electrical system checked?
What is the normal time for the light to come on, and how long does it take for it to go off?
Is this normal and what is the solutions?

Thanks for your input....

Tom L
Spring Lake, MI
95 E class 300D
126,000 miles

If the car is starting okay, you certainly don't need new glow plugs. The question will be answered in the fall. Your engine would probably start this time of the year with no glow plugs at all.

I suspect that your glow plugs are working okay, but the light is not right.

Depending on where you live, it will be October or so before you know if you have a real problem.

Good luck,

The glow plug light should come on when you first turn the key on and go out after a few seconds, indicating it is ok to start the engine. Mine does this each and every time, regardless of engine temperature. I have read (and believe it) that the system calculates the glow time based on ambient temperature, not engine temp.

The way your system is working is definitely not normal. You could probably find more information by searching for "glow plug relay". And you might get some diagnostic help from a professional tech if you post in the tech help forum. Unfortunately, the techs don't check this section very often.

Like Larry says, you'll be fine through the summer. But you'll need to get it fixed before the weather turns cold.

By the way, waiting for the glow plugs to warm up every time will reduce the cranking time and make life a little easier for your starter.

__________________
Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

Insertion #3

I have checked the relay... Sanded the contacts... They looked dirty... Applied voltage to each contact point (1-6) and found that #3 plug was at zero...

The light in the car still puzzles me...

I disassembled the relay and turned on the key and it activated right away and was on for 25-30 seconds(which I think is normal). The light in the car came on after the relay released the solenoid from the contacts.

I need to know if this is just a plug problem or something else?
Will one plug cause the hole system not to work?
How do I get to the glow plugs?
They seem to be under these huge intake manifold.
Is their something else that is missing from this situation?

Tom L.
Spring Lake, MI
1995 E class D
128,000 miles

My glow plug light used to come on when I turned the key prior to start. After starting it would then go out. This is normal operation. Recently, the glow plug light would not come on prior to start... but the car started anyway. After starting the glow plug light would stay on. I looked at the factory work shop manual and this situation is a result of the one or more bad glowplugs. Sure enough, when I checked the resistance on all the glow plugs one was a completely open, indicating a defective glow plug (#3). Unfortuneately, trying to replace this plug on my 91 350 SD looks to be a bear since the throttle linkages are in the way.
Plan to take the car to a local mechanic

Thanks guys for all your information!

I finally decided to take to repair shop and replace all
the glow plugs. I didn't want to wait to winter or fall to have my car not start. There were 2 glow plugs not working on the car out of 6. I didn't think the repair was something I could handle.

Tom L
Spring Lake, MI
95 E-class D
128,000 miles