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  #16  
Old 11-10-2012, 04:39 PM
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I've got the 617.91 manual and nowhere in there does it say that the glow plug timer varies according to temperature. It says that the light does, but that if the engine is not started, the plugs will continue glowing for up to 90+20 seconds.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #17  
Old 11-10-2012, 04:42 PM
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Quote:
Originally Posted by kerry View Post
I've had my 85TD at 35 below zero and the light never stayed on for more than about 20 seconds, if that.
Considering that the advertised glow period under high temp conditions can be as low as 22 seconds, it is easy to see that a 20 second light duration would be a problem if the entire glow period were not extended in colder conditions.

Last edited by qwerty; 11-10-2012 at 07:55 PM.
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  #18  
Old 11-10-2012, 04:45 PM
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Quote:
Originally Posted by kerry View Post
I've got the 617.91 manual and nowhere in there does it say that the glow plug timer varies according to temperature. It says that the light does, but that if the engine is not started, the plugs will continue glowing for up to 90+20 seconds.
Refer to post #2.

The 617.91 manual is not applicable to your 85TD.
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  #19  
Old 11-10-2012, 04:55 PM
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Quote:
Originally Posted by qwerty View Post
Refer to post #2.

The 617.91 manual is not applicable to your 85TD.
I never said it was.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #20  
Old 11-10-2012, 04:56 PM
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Quote:
Originally Posted by qwerty View Post
Considering that the advertised glow period under high temp conditions can be as low as 22 seconds, it is easy to see that a 20 second light duration would be a problem if the entire flow period were not extended in colder conditions.
Where is this glow period advertised?
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #21  
Old 11-10-2012, 04:59 PM
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Quote:
Originally Posted by qwerty View Post
The 617.95 Engine Service Manual describes the glow timer operation in great detail, complete with time/temp graphs.
I'm well aware of the engine manual since I have one. Nowhere in that manual does it suggest that the time of the glow is increased with temperature. The time of the light illumination is definitely increased with decreasing temperature.

I'm very sure that the glow plug time of 35 seconds is more than sufficient for the coldest expected ambient with an engine that has decent compression.

My original question was generated by this statement:

Quote:
Originally Posted by qwerty View Post
FWIW, the length of the glow period does not increase materially until the temp is well below freezing.
This suggests that you have actual data and are not simply speaking without any possible support.

But, my bad........apparently not.
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  #23  
Old 11-10-2012, 05:06 PM
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Quote:
Originally Posted by Brian Carlton View Post
I'm well aware of the engine manual since I have one. Nowhere in that manual does it suggest that the time of the glow is increased with temperature.
Did you look at the graphs?

Safety shut-off = glow duration.
Ready-to-start condition = end of light.

What is your interpretation of "The safety shut-off is no longer fixed but is the time up to ready-to-start condition (preglow indicator lamp goes out) plus 20-35 seconds?"

Quote:
Originally Posted by Brian Carlton View Post


This suggests that you have actual data and are not simply speaking without any possible support.

But, my bad........apparently not.
You have to look at the slope on the graph. See how it's sort of flat above freezing?

Last edited by qwerty; 11-10-2012 at 05:49 PM.
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  #24  
Old 11-10-2012, 05:13 PM
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Thanks for posting that graph. So as I interpret that graph, the 'timer' to shut off is fixed as a certain number of seconds after the light goes out. Since the light stays on for varying amounts of time, the total time energized varies according to temperature.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #25  
Old 11-10-2012, 06:00 PM
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Quote:
Originally Posted by kerry View Post
Thanks for posting that graph. So as I interpret that graph, the 'timer' to shut off is fixed as a certain number of seconds after the light goes out. Since the light stays on for varying amounts of time, the total time energized varies according to temperature.
That's the way I see it. Others, obviously, look at the same graph and reach a different conclusion. Perhaps the nearly parallel slope of the lines just doesn't fit their preconceived notions.
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  #26  
Old 11-10-2012, 06:50 PM
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Quote:
Originally Posted by qwerty View Post
That's the way I see it. Others, obviously, look at the same graph and reach a different conclusion. Perhaps the nearly parallel slope of the lines just doesn't fit their preconceived notions.
I'm going to test your theory this winter when we get down near zero degrees. Although the manual might be interpreted as you claim, I do not see any possible benefit from increasing the glow time above 35 seconds unless the glow light also increases above 35 seconds. I'm not aware of anybody in the last ten years who observed a glow light for 35 seconds or more...........even Kerry who has started the 617 at -35F.

I'm sure that somebody on here will correct me if I am mistaken.
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  #27  
Old 11-10-2012, 07:00 PM
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On a related issue: Does the motion of the key to the 'start' position override the timer/shut off circuit? In other words, the glow plugs remain energized after the light goes off and the engine is trying to start? There seems to be a consensus that once the key is released from the 'start' position, the plugs stop glowing unless there is an 'afterglow' installed. But if the engine takes a long time to start and the key is held in the 'start' position, does the timer cut off the glowplugs at the end of its cycle regardless of the fact that the engine is trying to start? If so, there's a benefit to starting the timer after the glow light goes out.
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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #28  
Old 11-10-2012, 07:14 PM
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Quote:
Originally Posted by kerry View Post
On a related issue: Does the motion of the key to the 'start' position override the timer/shut off circuit?
Yes.
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  #29  
Old 11-10-2012, 07:27 PM
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Quote:
Originally Posted by Brian Carlton View Post
I'm not aware of anybody in the last ten years who observed a glow light for 35 seconds or more...........even Kerry who has started the 617 at -35F.
Where is there any claim that the glow light remains illuminated for 35 seconds? Kerry's report is reasonably consistent with the data in the 617.95 manual, specifically, a light duration of as little as 23 seconds at -30*C.
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  #30  
Old 11-10-2012, 07:29 PM
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Here's the FSM on turbo 617 glow plug operation (78-80 and 81 onward)

http://mercedes.thatchermathias.com/w123CD2/Program/Engine/617/15-705.pdf


non turbo series type

http://mercedes.thatchermathias.com/w123CD2/Program/Engine/615/15-505.pdf

It talks about glow plug and indicator duration and safety shutoff of the different model years. Series type non turbo (pre 78) is different than 78-80 turbo, then it changed in 81. I do not see any mention for 85 and assume 85 is the same as 81 through 84.

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Last edited by funola; 11-10-2012 at 07:47 PM.
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