I've been starting 617's in cold weather for about 7 years now. I (and others on this forum) have noticed that in very cold conditions, the first starting attempt is always the best chance to get the engine going. Any subsequent attempts to start the engine, even if glowed as long as the initial attempt, are more difficult. Why is this the case? It almost seems as if subsequent attempts after the first are only successful once the heat from turning the engine over is enough to ignite the fuel. In other words, the glow plugs seem less effective in the later start attempts?
These thoughts are spurred by the fact that I started the 116 at 5 degrees this morning without pluggin it in after replacing a glow plug on Friday just to see if the glow system was working correctly again. I glowed for 75 seconds and engine fired after about 3 or 4 revolutions but I foolishly let off the starter before it was running steadily enough and it stopped. The next attempt, even with a 75 second glow and the engine previously running momentarily, took a good 30 seconds of cranking before a single cylinder fired and then another 15 seconds of cranking before enough cylinders were firing to keep it running.

Any good explanations out there?

__________________
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

It's the problem of continuous liquid fuel accumulating in the cylinders, thereby requiring that much more heat to fire.

Your best hope to start is in the initial 1-5 seconds. The prospects deteriorate based upon time.......not the number of attempts.

The deterioration with time is offset by the increase in the temperature of the cylinder due to repeated compression strokes.

Additionally, the deterioration with time is caused by decreasing battery voltage, thereby resulting in reduced crank speed and subsequently lower compression.

It's an interesting dynamic.

How were you able to accomplish this and overcome the relay timeout?

On the 116, that's the relay's timing. It stays on for 75 seconds. On my 85 TD it's only 28 seconds. The 116 has a physically different relay than the 85 TD. Don't know if this is a factor in the timing.

__________________
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

Isn't that liquid expelled each exhaust stroke, showing up as that grey unburned fuel exhaust? Is that liquid fuel just cooling down the cylinder causing the problem? If it is, would injection line heaters overcome the 'one try' problem?

__________________
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

Interesting..........does it use different glow plugs?

I believe that the liquid fuel must be sitting on the piston face and on the top of the cylinder to a significant degree. If most of it were expelled on the exhaust stroke, the issue wouldn't exist.

I'm sure injection line heaters would help significantly. The cylinder would much prefer fuel at 180° versus 0°.

No, unless I'm buying the wrong plugs. They're regular pencil plugs.
The relay is bigger and shaped different.

__________________
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

I'd be curious if a 30 second time gave the same results as a 75 second time.

Since it's the same engine, one might conclude that M/B learned that they didn't need the longer time and it served no benefit. The plugs can't heat the cylinder or the prechamber in any fashion..........only the air in the immediate vicinity of the plug.

How long was the glow light on for? How long after the glow light went out until the relay clicked off?

From what I understand from the FSM, the Ready-to-start condition (glow light off) is variable depending on ambient temps and the time frame between the ready-to-start condition until the relay clicks off is fixed.

Maybe the 5˚ temp caused a longer time for the ready-to-start condition?

__________________
Chad
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys

Glow light is on longer when it's cold on both vehicles but the timing of the relay seems independent of the length the light stays on. It's always at 75 and 28 seconds respectively.
It's hard for me to conduct a comparative experiment on the length of glow because the 85 starts better in cold weather than the 79 SD. Don't know the reason for this. My impression at the moment is that the 116 starts easier with the full 75 seconds rather than starting when the glow light goes off.
I think the 116 relay senses the temperature in the head and the 85 sense it at the relay itself.

__________________
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

That's right, I remember reading that now. Pre 1980 is a coolant temp sensor IIRC.

__________________
Chad
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys

The comparison would be strictly with the SD. Does 75 seconds allow a faster start than 30 seconds? I'm quite sure that 75 seconds beats the point where the glow plug light is extinguished.

According to the FSM charts and text, it looks like 1978 & 79 models glow 90 + 20 and 50 + 10 for 1980.

The charts show that the glow plug temps max out at 50 seconds, but can have extended glow until up to 80 seconds.

__________________
Chad
2006 Nissan Pathfinder LE
1998 Acura 3.0 CL
OBK#44
"Pleasure in the job puts perfection in the work." - Aristotle (384-322 B.C.)

SOLD
1985 300TD - Red Dragon
1986 300SDL - Coda
1991 - 300TE
1995 - E320
1985 300CD - Gladys

My wife usually drives the SD and I just started experimenting with the 75 second glow when it had glow system problems last week. I worked on the car a fair amount early last winter when I first bought it because it wasn't starting below about 28 degrees. I got it to the point where it would start without a heater at 10 degrees. At that time, I was attempting a start when the glow light went out (probably about 25 seconds). My impression with the 75 second glows recently is that it was starting better than it did a year ago. I think I can say with some certainty that the 75 second glow helped when one glow plug was not functioning since my wife couldn't get it started (she has been starting when the glow plug light went off) and I could get it started with a 75 second glow.
I may be able to conduct some experiments with a fully functioning glow system over the Xmas break when my wife is not driving it to school.

__________________
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