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  #1  
Old 01-27-2008, 10:25 AM
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Am I killing my glow plugs?

I replaced all glow plugs in my 84 300D last winter. With the cold weather we have had recently I have been going through three glow cycles that are extended maybe ten seconds after the light goes out then starting the car. I had the first glow plug failuer last week (no GP light) I found the #1 PG to be bad and replaced it. I now have no glow plug light again but haven't had time to check it out. I need to know if these extended glows are killing the plugs or if this is just a fluke?

Thanks,

Mike

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  #2  
Old 01-27-2008, 10:27 AM
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Is there a good reason why you are performing three glow cycles?

What happens if you let the plugs glow for 30 seconds...........once............and attempt to start the engine?

How "cold" is cold?
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  #3  
Old 01-27-2008, 10:44 AM
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Hi Brian thanks for posting,

I am performing three glow cycles due to the fact it will not start otherwise. The weather has been down to the single digets. I can start it 30F and above pretty easily but 20's and lower difficult to start. I am using synthetic Rottella
a new battery, but reciently found out the block heater is not working. I have not adjusted valves for 20K and know it needs to be done, the car is approaching 250,000.

Mike
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  #4  
Old 01-27-2008, 10:50 AM
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What brand of glow plugs did you install?
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  #5  
Old 01-27-2008, 10:59 AM
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From what I have learned from other members: Synthetic oil makes cold starting easier. Is the starter cranking up to speed. If not clean your electrical connections and check again.
When was the last time the injectors were tested. That pin ball in the combustion chamber helps marginal injectors to preform OK but it has to be hot to do so and it will not be during a cold start.
Might be time for a compression check (after the valve adjustment).
When you changed the glow plugs did you ream out the carbon?
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  #6  
Old 01-27-2008, 12:17 PM
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Luck of the draw in a glow plug failure of one plug in a year type of thing could also be a factor. The three cycles are perhaps not causing a lot of additional stress or just a little or maybe a lot. We probably lack this knowledge on site but the plug manufacturer might have the data. Failure of one plug in one cycle aplications after one year is not uncommon either.
If you locate and change the failure plug yourself no large financial outlay occurs. You are going to continue the three cycles most likely as a given if the car will not start otherwise.
When the weather warms up or you have a heated garage do a complete tuneup. It is time intensive rather than money. Valve adjustment, chain stretch, injection pump timing, etc.etc.
You know the manufacturer at the time of introduction wanted all these items looked at anyways about every thirty thousand miles. Some cars out there have far exceeded this milage it seems with nothing done if it still runs. As a bonus you may have more power as well. Not that you would particularily like or need it.
Symptoms like yours can be the result. There is no way of knowing unless you either know when they were done or do it. Can be many things causing your three cycle requirement. Some are easily addressable others are not.
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  #7  
Old 01-27-2008, 12:25 PM
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Quote:
Originally Posted by Diesel911 View Post
Might be time for a compression check (after the valve adjustment).
A compression check isn't gonna help you start your car easier, and I don't think you'll run out and rebuild the engine based on results.

If you are using Autolite glow plugs that could easily explain the failure. If Bosch, well, they all fail after a while. Your's will not last as long with multiple duty cycles as that simulates more time in the car. What is the saying, "The light that burns the brightest burns out the fastest".......
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  #8  
Old 01-27-2008, 12:44 PM
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Originally Posted by mike0000 View Post
Hi Brian thanks for posting,

I am performing three glow cycles due to the fact it will not start otherwise. The weather has been down to the single digets. I can start it 30F and above pretty easily but 20's and lower difficult to start. I am using synthetic Rottella
a new battery, but reciently found out the block heater is not working. I have not adjusted valves for 20K and know it needs to be done, the car is approaching 250,000.

Mike
Single digits are tough on older engines. Unless you're quite fortunate and the valves have not worn significantly, these engines will struggle at that temperature.

Adjusting the valves to spec will definitely assist in a cold start. If the intake valve is just the slightest bit below spec, it can hang the valve at those temperatures. In fact, I'd adjust the intakes to .005" to be on the safe side.

I'm not sure it you want to spend any money, but, the 617 in the SD will start in one second at 0°F. and it has 208K on the clock. The new valves at 185K made all the difference in the world in terms of fuel economy and cold start performance. It's $1K well spent.
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  #9  
Old 01-27-2008, 01:20 PM
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Quote:
Originally Posted by mike0000 View Post
Hi Brian thanks for posting,

I am performing three glow cycles due to the fact it will not start otherwise. The weather has been down to the single digets. I can start it 30F and above pretty easily but 20's and lower difficult to start. I am using synthetic Rottella
a new battery, but reciently found out the block heater is not working. I have not adjusted valves for 20K and know it needs to be done, the car is approaching 250,000.

Mike
Are your first two glow cycles all the way until the plugs cut out? There's a separate timer for the light than for the plugs. My light goes out after 10-20 seconds, but the plugs keep glowing for a minute or so as evidenced by the dome light snapping brighter after that long. Once I realized that, I stopped recycling the plugs when the light went out and just let them glow a bit longer than the light. Made the engine a lot easier to start. How much longer depends on how cold it is out, but try starting with double the time the light stays on.

Heating and cooling cycles are pretty stressful so may be killing the plugs early. Since the idea is to get them glowing hot so the fuel ignites when it touches them, glowing longer is more effective than turning them on and off multiple times.
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  #10  
Old 01-27-2008, 01:41 PM
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Exactly, many people don't realize that the glow plugs stay on for another 25-30 seconds after the light on the dash goes out. So just set it to glow, and wait about 30 seconds, then try to start it. Also, do not press on the throttle AT ALL, until the engine begins firing/struggling, then give it some throttle to help it get going. Giving throttle while cranking at those temps (before the engine starts firing) will negate things and make it harder to start. Also, if its been 20k since a valve adjustment, you need to take care of that too, it makes a lot of difference when trying to start in the single digit temps.

Make sure you use the good Bosch glowplugs, the cheap autolite plugs are just about worthless.


Our 300D has nearly 226k on it, and it will fire off in 1-2 seconds with no assistance (no block heater, no giving throttle...etc) in single digit temps with only a 7-10 second glow.
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  #11  
Old 01-28-2008, 03:37 AM
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Originally Posted by pawoSD View Post
Exactly, many people don't realize that the glow plugs stay on for another 25-30 seconds after the light on the dash goes out.
Only IF the relay has been modified for it to have that function. W116, W123 and W126 models turn off the glowplugs the instant you hit the starter.
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  #12  
Old 01-28-2008, 09:41 AM
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Originally Posted by ForcedInduction View Post
Only IF the relay has been modified for it to have that function. W116, W123 and W126 models turn off the glowplugs the instant you hit the starter.
Lance, you're thinking "afterglow". He's simply referring to the time after the light goes out and before the starter is engaged.

The standard, unmodified relay functions as he described it.
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  #13  
Old 01-28-2008, 10:02 AM
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Cool Hmmmm...

Quote:
Originally Posted by pawoSD View Post
Giving throttle while cranking at those temps (before the engine starts firing) will negate things and make it harder to start
Really? I read somewhere (maybe on this forum) that one should fully depress the pedal (too open the rack or something, if I remember it correctly) then lift up to about the halfway mark before even starting the glow process. I thought it strange, as on my jetta, I was told not to even touch the pedal until the car's started. I've been doing this ever since I got my Benz!

So far, I've never had problems starting, but I've sometimes forgotten the pedal and the starting has been exactly the same. It doesn't really get cold out here in Metro Van, but today was about -4 when I started, predictably with the same result every morning.
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  #14  
Old 01-28-2008, 10:12 AM
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Originally Posted by zu! View Post
Really? I read somewhere (maybe on this forum) that one should fully depress the pedal (too open the rack or something, if I remember it correctly) then lift up to about the halfway mark before even starting the glow process. I thought it strange, as on my jetta, I was told not to even touch the pedal until the car's started. I've been doing this ever since I got my Benz!
The FSM instructs the operator to press down halfway and hold when in very cold ambients. The intention is to insure that the engine has sufficient fuel to run when very cold. This works on new engines with high compression.

With an older engine, if more fuel then required is dumped into the cylinder, the heat of compression is lost in the attempt to warm all the cold fuel. Any chance of starting is lost when you're in a marginal situation.

So, if you've got an engine with less than stellar cold performance, it's preferable to use no pedal until the engine is actually running on it's own.......and then apply some pedal to keep it running.

I got stuck in this exact situation with two bad glow plugs. Had to crank it for 30 seconds with no fuel until it was running on the combination of the starter and the engine. Then, took a chance........gave it a touch of fuel and let the starter go..........and it was running on it's own.
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  #15  
Old 01-28-2008, 10:44 AM
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Yeah, our 300D must have amazing compression as it will actually start faster with some throttle when starting at super cold temps, where my SD will....keep cranking till the battery is dead. I am sure my engine has lower compression, but it will still start with about 7-8 seconds of cranking even at 0F....so its not a "lost cause" yet....its been that way the last 60k....so it will probably still last a while....I start mine by staying off the pedal till its running with the starter then I give some throttle.

The 300D will start and idle smoothly at 0F without ever touching the throttle at all, you don't even have to help it keep going. My dad's SD is the same way....both have no visible blow-by with the cap off....mine has lots.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 90k - mine - (OC-91,200)
'17 Metris(VITO!) - 18k - wifes (OC-25k)
'01 E320 Wagon - 161k - mine (OC-165,000)
'01 E320 - 180k - dad's (OC-182,500)
'07 E350 Wagon - 134k - dad's (OC-139,500)
'01 SL500 - 56k - dad's (OC-59,000)
'16 E400 4matic Sedan - 81k - Brothers (OC-88,000)
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