Is my glow system going bad? ('85 300TD) - PeachParts Mercedes-Benz Forum

IZELJIC · #1 05-30-2003, 09:46 PM

My glow light sometimes does not come on when I turn the key to ignition position. When it does come on it only stays on for about 2 seconds (when the car is cold) but when the car is warm it only stays on for less than a second. The weather has been quite warm lately (50's in the morning and 70's during the day) and the car always starts right away. The glow plugs have been replaced about 5K miles ago (about 3 months ago). Is my relay going bad? Can I test it somehow?

I appreciate your help, Igor.

P.E.Haiges · #2 05-30-2003, 11:52 PM

IZELJIC,

Your GP system is not going bad, just the timing section of it. The dash light does not reflect how long the GP stay on, its just how long you should wait until you turn the key switch to the start position.

As long as the engine starts easily, I wouldn't do anything. You just have get used to how long to wait to energize the starter.

Were you having starting problems before you replaced the GP?

P E H

IZELJIC · #3 05-31-2003, 12:02 AM

Prior to replacing the glow plugs the car sat for a few years and I rescued it from being burried under feet of snow. It was not starting at all until I replaced the glow plugs and it cranked right up. The only other problaem which I had was a bad battery which I replaced. The car always starts on first try and normally I wait 10 seconds even after the glow light goes off before starting it (especially when the car is cold).
P.E. Haiges - Why did you ask whether I had starting problems prior to installing new glow plugs?

Thanks, Igor.

P.E.Haiges · #4 05-31-2003, 08:21 PM

IZELJIC,

I was wondering if you had a hard start problem and if the new GP fixed it.

I had '80 300SD and it always took a few cranks to start. Then I got a '79 300SD and it usually started on the first crank. I noticed on the '79 300SD the GP light stayed on longer. So I tried waiting about another 10 seconds before trying to start to '80 300SD and it now also usually starts on the first crank.

So the GP timer can get out of calibration. I suppose it could be fixed but its easier just to wait the correct time to allow enough time for the GP to preheat. If the timer worked correctly, you would have to wait the same amount of time anyway, so nothing is lost.

P E H

IZELJIC · #5 06-01-2003, 02:21 AM

So is the glow light timer different from the actual glow plug timer? If I understand you correctly even if the light goes of after one second (or if it even does not come on at all) the glow plugs are still working? The car still keeps staring as before so now I am really puzzled.

P.E.Haiges · #6 06-01-2003, 02:55 AM

IZEJIC,

Yes, the GP stay on for about 40 seconds if you don't energize the starter but the GP are turned off as soon as the starter is energized. The timing of the GP is independent of the dash light and the GP work regardless if the dash light works or not. That is why your engine starts easily even though your dash light doesn't work correctly. The dash light is supposed to be calibrated to the temperature of the engine: cold on longer time, hot on shorter time.

In my '79 300SD, the dash light works intermittently but the engine always starts immediately as long as I wait long enough for the GP to preheat.

P E H

P.E.Haiges · #7 06-01-2003, 10:52 AM

IZELJIC,

Yes, the dash light timer is different than the timer that energizes the GP.

The GP timer energizes the GP for about 40 seconds unless the key us turned to the start position. Then, as soon as the starter is energized the GP are turned off and the started cranks the engine.

The dash light timer is supposed to be calibrated to the temperature of the engine, I.E. the colder the engine, the longer it should stay on. But some times this timer gets out of whack like yours does. But it does not affect the actual operation of the GP.

So if you wait long enough for the GP to preheat, your engine will start easily regardless of what the dash light does.

P E H

IZELJIC · #8 06-01-2003, 05:44 PM

Once again......you guys are awesome. Sometimes I can't sleep at night because of this car.

Thanks, Igor.