I have a '68 220D which is slowly getting road worthy thanks to this resource. The owner's manual and service manual give recommendations for how long to preglow the glowplugs when cold-starting the engine based on ambient temperature. Do you think they intended the timing to "start" when you first electrify the circuit, or when the little glowplug resistor on the dash begins to glow (about 10 seconds later with my car)? The wording is a bit vague. At 20C, they recommend about 10 seconds of preglowing. If you start timing at the pull of the knob, 10 seconds is not long enough for my engine to start. But if you start timing when the resistor begins to glow (a total of 20 seconds), then it starts up just fine.

Obviously, I just need to do what works, but I am trying to use this as an indirect measure of engine health. Thanks for your advice.

with the old resistor wire plugs, I'd wait until the indicator glows before beginning to count. they produce hardly any heat for the first 7 or 8 seconds.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Hey Shorts,
There is no such thing as a dumb question !
Cant guarantee that the answers will always be as correct as vstech has been this time !!!
Much better to ask a question & find out, than to waste $$$ unnecessarily.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

That's a good question. Since the plugs are in series, I would assume that the indicator is the last bit to get energized.

That being said, I've been giving my W115 a 15 count with the indicator starting to glow at 12 seconds. On hot (90F+) days last summer it wouldn't need any glowing at all.

Over the winter months (at or slightly below freezing), I was counting to 30 before lighting it off and would have to "goose" the accelerator to prevent it from stalling. This was before the IP rebuild, so it might react differently in the cold now.

For reference regarding comparative engine health, my compression is around 300psi across all cylinders and I'm on pace to burn about 1 quart of oil per 1000 solid highway miles or, as best I can tell, about 1 quart per 1500-2000 mixed driving miles. From reading these and other boards 1,000 miles per quart was still within spec even for a new engine. Someone chime in if otherwise.

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Off topic I know, but switching those series loop plugs with the retrofit pencil plugs will make a huge difference in how the engine starts. Not sure anyone on here has made the switch on the old gorilla knob system, but I think it's possible and probably pretty simple.

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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

The little in-dash glow indicator is a clever little device that mimics the action of the glow plugs. It takes a few seconds for the indicator to reach red-hot temperature (unlike a lamp that becomes bright almost immediately) and so I would think the same is true for the glow plugs themselves.

I would start counting once the indicator gets up to temperature.

There's a how to floating around. If I recall, it requres some rewiring and the glow indicator is now out of the loop.

At this point, I'm content with the series. These W115s are survivors and mine will be as original as possible. I also see the gorilla knob as part of charm.

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1974 240D "Boldie" 170K.- New timing chain/freshly rebuilt IP/replaced valve seals/injectors/upgraded stereo/new Bilsteins with Yokohamas/fresh paint and rocker panels plus lots of welds.

Personally, I'd keep the gorilla knob but just put in the different plugs. I think manually controlled glow cycles are superior to automatically controlled ones.

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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

Thanks for the input/advice. My understanding is that if you switch to pencil GPs, you have to lose the "salt-shaker" indicator, which is something the traditionalist in me is not willing to do just yet.

Also, when GPs are in series, they all experience the same current simultaneously. And assuming the resistances are similar, they should also experience the same voltage drop simultaneously. So, if the resistances are similar, the dash resistor should glow at about the same time as the others.

Recently, I have had to give the vehicle a little throttle when starting, which is what troubles me. When the car was last used in its previous life (10 years ago), this was not the case. When the oil pressure is low, I would rather not be blipping the throttle (I am trying to get used to not calling it a gas pedal).

My next big step is to adjust the valves and then check the compression. But these jobs seem to amplify (e.g., while I have the GPs or injectors out, I might as well ... (fill in the blank)). So I am taking it slow right now.

Once you do get the car on the road, a useful aid for the long term is a chart or table that shows ambient temp vs glow time. Since each 220D will be a bit different, this is something that you will have to create using experience over the course of a year. Thankfully your winter temps are probably not very severe, and won't stretch the table out to infinity!!!

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

I'm with you on resisting the urge to retrofit the pencil plugs on my 240D. When you have the plugs out be sure to ream out the holes to remove as much old carbon buildup as possible. I didn't do that and i'm still having issues with cold starts (multiple glow cycles)