Glow plug timing on 123's - PeachParts Mercedes-Benz Forum

kerry · #1 11-26-2007, 12:45 PM

I guess I'm a slow learner. I just figured this out. In really cold weather (say 5 degrees or below) I've noticed that even if I double glow, if the engine doesn't start within a second or two, it takes about 30-45 seconds of cranking to get it going and it usually begins firing on just one or two cylinders with the starter helping it for a while. I now think that this occurs because the glow plugs shut off when the key goes to the start position. So, in really cold weather, the residual effect of the glow plugs is lost pretty quickly and you end up starting just on the heat generated from cranking the engine.
It seems it would be much better if in cold weather a person could keep the glow plugs energized thru the starting cycle. This would be much easier on the starter and battery.
Has anyone tried this in cold weather with a 617 and noticed any difference in starting ability. I noticed Lance indicated in the other thread on glowing that he has a manually controlled glow plugs. Does this improve starting in very cold temperatures Lance?

THIS POST CONTAINS MISINFORMATION. The glow plugs continue to glow as the starter is turning.

toomany MBZ · #2 11-26-2007, 02:37 PM

Are you letting the GP's go through a complete heating cycle? Even after the dash light goes out, they are still glowing. If you listen closely, you should be able to hear a "thunk" for under hood, that's your relay timer. Takes around 30 seconds total.

kerry · #3 11-26-2007, 02:43 PM

Yes. But at 35 below zero that heat dissipates very quickly. I've even let them go thru the complete cycle twice.

pawoSD · #4 11-26-2007, 02:48 PM

When its that cold its critical that you have excellent plugs and possibly an afterglow relay (keeps the plugs on a while after startup) to assist it in running.

Also critical is the way you crank.

Give it a long glow (perhaps 25-30 seconds, then begin cranking, BUT do NOT press on the pedal at all....keep cranking till it starts firing on its own, then give it some throttle and once its going release the key, then hold the idle around 1000-1100 or so for a minute or two, especially at temps like that. Thats cold!!! Pressing the throttle while cranking in the cold puts fuel in the cylinders and will destroy the attempt at starting.

omne207 · #5 11-26-2007, 02:51 PM

i found when i had to work at 5 in the morning going for a drive for like 20 min the night before would help keep the engine warmer for the morning
but i live in the desert so who knows if that may help

Brian Carlton · #6 11-26-2007, 02:54 PM

Additionally, the primary reason the engine won't start after a few seconds is the fact that very cold fuel is being injected into the cylinder. This dissipates any heat that was present and results in a long slow crank time.

Now, if you could find a way to fully shutoff the fuel for the first five seconds of crank time so that the cylinder could warm a bit.........now, you'd have a good solution.

pawoSD · #7 11-26-2007, 02:55 PM

Quote:

Originally Posted by omne207

i found when i had to work at 5 in the morning going for a drive for like 20 min the night before would help keep the engine warmer for the morning
but i live in the desert so who knows if that may help

When its -35 the engine will go from operating temp to completely frozen in less than 3 hours....so it'd probably not make a difference. And, it'd probably not be at operating temp to begin with.

Mine is lucky to hit 70C when its real cold out....probably need a thermostat though.

kerry · #8 11-26-2007, 04:11 PM

Ok, so here's my experiment. It depends on the fact that engaging the starter at the junction box on the fender does not shut off the glow plugs since the ignition switch is still in the glow position. Is that correct?

Wait for a very cold day.

1. Put a Mity Vac on the shut off valve and pull a vacuum

2. Glow the plugs with the ignition switch for a full cycle, then reglow.

3. Spin the starter from the junction box on the fender for 5 or 10 seconds.

4. Release the vacuum from the shut off valve while continuing to turn the starter.

Theoretically, the car should start more promptly than under normal conditions.

Brian Carlton · #9 11-26-2007, 04:23 PM

Quote:

Originally Posted by kerry

Ok, so here's my experiment. It depends on the fact that engaging the starter at the junction box on the fender does not shut off the glow plugs since the ignition switch is still in the glow position. Is that correct?

Wait for a very cold day.

1. Put a Mity Vac on the shut off valve and pull a vacuum

2. Glow the plugs with the ignition switch for a full cycle, then reglow.

3. Spin the starter from the junction box on the fender for 5 or 10 seconds.

4. Release the vacuum from the shut off valve while continuing to turn the starter.

Theoretically, the car should start more promptly than under normal conditions.

The vacuum shutoff activation with the Mityvac would certainly be a good idea.

Remember, however, that we're talking about very cold temps (below zero) with engines that have some wear.

My SD starts in 1 second at 0°F. after a full glow cycle. So, none of these modifications are required unless it's much colder than 0°F.

pawoSD · #10 11-26-2007, 04:26 PM

My SD starts in about 6-8 seconds at 0F

Does that make it 6x as worn out?

Brian Carlton · #11 11-26-2007, 04:28 PM

Quote:

Originally Posted by pawoSD

My SD starts in about 6-8 seconds at 0F

Does that make it 6x as worn out?

........old valves.........

barry123400 · #12 11-26-2007, 04:51 PM

It's pretty hard on the engine and electrical stuff not to employ the block heater in some fashion if at all poissible when really cold. If you really want to radically lessen the cold start time without it investing in a high speed aftermarket starter is kind of mandatory.
This also helps the even lower temperature starting ability to some extent as well .Your present starter may have dropped off a little rpm wise from it's new condition too..
Also the employment of synthetic oil is another given.
It is a good ideal to check the injection pump timinng if not known. The timing tends to retard with age and wear on these engines. In cold temperatures that is absolutly the last thing you want on a diesel.
As Brian suggests even improper valve clearances can compound the problem mind the natural wear over time.
Come to think about it a well constructed engine blanket with reflective foil kept in a plastic bag should extend the period until the block cools off to quite an extent. Reflective foil will bounce the radiant heat component back to the block as well as lessen convection losses to some extent.
A thermometer under the blanket would give you the new cooling curve. If the block can sustain four hours with no protection till it reaches the ambiant temperature for example . It would not suprise me to see that increased to six hours with the refllective component. I am not quite sure why science seems to have difficulty with rating reflective surfaces. I know they work well in general and incorporate them in various projects of mine.
A couple of simple tests can confirm their value though for any non believers. Have you ever noticed you can lift the foil over a turkey in the oven as soon as the door is opened and it seems cool to the touch? If you touched the roasting pan you would get a burn. Or place a heat source in front of even household kitchen foil. Even close to thje heat source the foil remains cool. You can even phisically feel the re radiated energy being absorbed by your hand close to the heat source Yet the foil itself is normally an excellent conductive thermal transfer agent.
A larger portion of the heat is being returned to the source direction. Has to be more than just the radiant component or the foil would warm up. This is a poor but informative trial. You want a very high percentage of aluminium in the relective surface for a blanket. Household foil is too much of an alloy mix to be nearly as effective. One should at least experiment as this approach is useful for many applications in life.
No I have no alcoa shares in our very limited holdings.

vstech · #13 11-26-2007, 04:55 PM

yeah, at -35F, NOTHING helps. a blanket, covering the engine, with a block heater plugged in, and an additional oil pan heater running, with a fuel tank heater going, and parked on a heat pad, would be nice, other than that, you are looking at a LOT of cranking.

barry123400 · #14 11-26-2007, 05:42 PM

I totally agree at -35 F without major assist it might take dynamite to start it. The engine technology is just too old.
For higher temperatures say - 10 F where you were caught out with a cold engine I wonder if setting a propane torch into the intake manifold inlet on non turbos or removing the U tube and pouring heat in for a few minutes might get you past a somewhat marginal starting temperature? I believe some diesels incorporate at least one glow plug in the intake manifold for simular effect. Any comments?
I believe the turbo is out of the line with the u shaped connector removed. I also imagine if there was another body available to man the torch you could keep feeding heat into the intake manifold while cranking.
This leads me to wonder if anyone has ever bothered to add an additional glow plug in the manifold of a 616 or 617 to heat the input air charge before cranking the engine? Someone should experiment as it is a low cost thing. I just have too many things on the go to follow up all my thoughts. But keep records as it is bound to be benificial to some extent. Just wonder if enoughh to justify the trouble?
From time to time I regress somewhat to try to find a fairly simple approach to up the fuel milage somewhat on these old buggies.
So far no really good brainwaves in this area. In fact I would refuse a test on brain activity if offered.
I dislike my personal failures except perhaps for the learning experience incorported in it.
Ulimatley far too many of my seeming abstact at the time ideals ultimatley seem to bear fruit to discontinue thinking and acting upon them. Or seem to directly lead to something else. That makes me a sucker for punishment I suppose.

kerry · #15 11-26-2007, 05:55 PM

I think Lance was working on modify a Dodge Cummins intake heater to adapt to his 617. Not a glow plug, but close.

I did try a propane torch and a hair drying blowing in the intake of my 77 300NA when it had loop plugs and was harder to start in cold weather. Didn't seem to make any difference.

I was thinking about these issues as avenues of pursuit should a person be caught in cold temperatures unawares.
The one time I started at 35 below I was caught off guard. I had no block heater and travelled to the mountains when it was in the 50's in Denver and failed to check the weather forecast. It was 35 below two days later in the mtns. I was able to get it started and running on 2 or 3 cylinders for a minute or so before the gelled fuel stalled it. I didn't realize that I did not have winterized fuel. I did not know that Denver does not sell winterized fuel. The mountain towns do sell winterized fuel.

Had I been in that situation knowing what I now know and with winterized fuel, since you only have one chance to start it in those conditions before the battery died, I'd have glowed the plugs a few times, put a piece of vacuum hose on the shut off valve and sucked on it to keep the fuel out of the cylinders and cranked it for about 30 seconds before letting the fuel flow. I think that would have given me the best chance of getting enough heat to get going.

Of course now I have a block heater and a magnetic pan heater which I would put on the fuel tank.