Glowplug light takes to long to go out? - PeachParts Mercedes-Benz Forum

Buzz Gunderson · #1 01-25-2004, 06:29 PM

I was reading in this forum today about people having to wait 5-10 seconds for their dashboard glow plug lights to go out before they start the car. The light on my 1978 240D takes 75 seconds when the engine is warm, and 20 seconds or less when it is cold (winter temperatures outside). I'll live with these time if they're normal. If not, does anyone know what kind of problem they signify? As always, many thanks for any insights this bunch of experts can offer.

whunter · #2 01-25-2004, 08:11 PM

Hello Buzz Gunderson
I am a new owner of a 300 SD.
My glow plug light was over 120 seconds.
January 23-2004; I tested my glow plugs and found two dead and the rest had a wide resistance range, ordered five new glow plugs, will install January 26-2004.

To answer your question:
Glow plugs or relay.
Hope it is the glow plugs, the relay is higher.

Have a great day.

Gilly · #3 01-25-2004, 08:50 PM

The light on the dash just switches off when the optimal time is reached to crank. That 75 second figure you give is about how long the system works until the system is actually disabled (the relay actually shutting off the glowplugs).
The system determines how long the light should stay on by a coolant temperature sensor, so that could be the problem, maybe a bad sensor.
A few basics for you to check are a loose glow plug wiring connection, and it certainly wouldn't hurt to have a load test done on the battery and check the connections on the battery.
I agree that when you are having preglow problems it's a good idea to know that the glowplugs are all working good, I like to do the current consumption test, which is a bit of a hassle on the series-wired plugs. With series wired you may be tempted to do a voltage drop test instead, published figure is .9 volts drop per plug.
More than likely I'd guess it's going to be either the coolant temp sensor or the relay. My basis for thinking this is that you don't state you actually have a problem STARTING the car, it's just the preglow light that's the problem.

Gilly

PS just to clarify, just because the light goes out doesn't mean the glowplugs are shut off, this doesn't happen until about 1 minute after being switched on, + - 20 seconds.