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  #1  
Old 01-23-2019, 08:08 PM
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1984 300CD, won't start in coldish temps.

The temps are only about 25f (-4c) at night and the car is in an unheated garage. Some of you have much colder temps. The glow plugs are a few years old. Could be that. How do I test glow plugs? I suspect that the block heater isn't working. Would help to have a block heater.

What is the best way to test glow plugs? What are some other suspected causes? This car has been my dependable daily driver since 2012.

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  #2  
Old 01-24-2019, 12:08 AM
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testing glow plugs.

take them off the car, link them together with the resistor wire and apply a thin dab of oil on the elements and then put 12v car battery to them, you'll see the smoke effect if they are successful in being clean and good contact/ working order. see video

https://www.youtube.com/watch?v=kUgO6Stx27I

this is if your engine is the older style of glow plug system.


If it's the newer style, i believe each plug uses 12V ( please correct if wrong ) and you can test each plug with a car battery, just the tiniest bit of oil upon it to see the smoke burn off if it's working.

clean them afterwards and reassemble the good ones
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  #3  
Old 01-24-2019, 01:00 AM
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Thanks Math. I'll do that tomorrow. In '84 we have the newer type. I assume that a direct 12v will do it. I can say that when I turn on the plug relay when they are installed, the battery voltage drops about 1/2 volt. To me that says they are drawing amps.
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  #4  
Old 01-24-2019, 01:55 AM
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Pencil glow plug broke inside cylinder!! 1984 CD

Car wouldn't start so I started pulling the glow plugs. Imagine my surprise when I pulled the no. 1 glow plug and the glow plug tip didn't pull out with the rest of the glow plug. Now, I'm worried that if I stick something in there to try to fish it out, i'll push it further inside the cylinder. What do do now???
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  #5  
Old 01-24-2019, 08:17 AM
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Easiest way is a multimeter. See which wires have extremely high resistance and you’ll figure out which one is bad with a lot less mess and effort. You’re also supposed to pull the glow plugs out hot. Not cold.
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  #6  
Old 01-24-2019, 03:30 PM
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Quote:
Originally Posted by gregp1962 View Post
Car wouldn't start so I started pulling the glow plugs. Imagine my surprise when I pulled the no. 1 glow plug and the glow plug tip didn't pull out with the rest of the glow plug. Now, I'm worried that if I stick something in there to try to fish it out, i'll push it further inside the cylinder. What do do now???
Might be difficult consider the block is iron, but they do make magnetic tipped extractors. I would get one to try and pull it out.

That's most likely your problem there. I wrote up this little tidbit on cold starting that's useful once you have your glow plugs fixed.

Since you pulled one that was falling apart, I would get 5 new plugs and replace them all. They're cheap enough for the insurance.

---

If your glow plug light is turning on when you start the car, there's a high probability your plugs are working alright.

There's absolutely no need to take glow plugs out of the car to test them. Get a multimeter and follow this guide https://dieselgiant.com/glowplugrepair.htm.

Once you've checked that out, do the following:

1. Check your glow plugs, glow plug relay fuse, and battery health
2. Oil change to 5w40 weight oil with new filter.
3. Perform a valve adjustment -> very very important if you haven't done this recently.

That order will restore your cold starting ability. If it doesn't, I would seriously question the health of the motor.
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  #7  
Old 01-24-2019, 04:48 PM
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I would have started with the valve adjust .

You can test the glow plugs from the relay, use the connector unplugged .

? Is there any crud or dark fuel in the clear plastic fuel intake screen next to the injection pump ? .

Let us know how the broken glow plug tip removal goes.....
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  #8  
Old 01-30-2019, 01:30 PM
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OK, the glow plug tip in cylinder #1 was broken off inside the pre chamber. I ordered the tools from Mercedes Source. They came very quickly as usual. The tools he sells made it very easy to pull the pre chamber. It would be impossible without these tools. MAKE SURE THE GLOW PLUG TIP IS NOT IN THE WAY WHEN PULLING THE CHAMBER.

I pushed the glow plug tip all the way inside before pulling the chamber and put everything back together. There is no way a vacuum or magnetic puller would have gotten it out. The pre chamber NEEDED to come out.

But, I still have the problem of not starting. Maybe I'll adjust the valves next. It has been over 20k miles since the last valve adjust.
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  #9  
Old 01-30-2019, 01:37 PM
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To avoid breaking off the tips (they fragile... not solid metal but a hollow tube with a coil spring inside) use penetrating oil liberally and be very careful backing them out. I'd remove the hard fuel lines to make it easy to get a straight shot at the flats on the plug. Then put in all new bosch plugs. There are reamers too to make the hole bigger but I have never used one.
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  #10  
Old 01-31-2019, 12:37 AM
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Quote:
Originally Posted by t walgamuth View Post
To avoid breaking off the tips (they fragile... not solid metal but a hollow tube with a coil spring inside) use penetrating oil liberally and be very careful backing them out. I'd remove the hard fuel lines to make it easy to get a straight shot at the flats on the plug. Then put in all new bosch plugs. There are reamers too to make the hole bigger but I have never used one.
This is good advice.

And.... put in a full new set of Bosch glow plugs and give it a whirl. Chances are it'll fire up. If not, it's time to look elsewhere. Does it start in warmer weather? If it's 25F at night, during the day it's probably not cold enough for a block heater to really matter.
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  #11  
Old 01-31-2019, 02:58 AM
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I have taken a propane torch,and turn gas on into intake to start my diesel at 12 f with no glow plugs working.don't use ether
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  #12  
Old 01-31-2019, 09:48 AM
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Quote:
Originally Posted by gregp1962 View Post
Thanks Math. I'll do that tomorrow. In '84 we have the newer type. I assume that a direct 12v will do it. I can say that when I turn on the plug relay when they are installed, the battery voltage drops about 1/2 volt. To me that says they are drawing amps.
12 volts is fine on the pencil type Glow Plugs used on the 617 type engines.

What you want to see is the tip of the Glow Plug get yellow hot. If it gets hot in the middle as the one in this picture that plug is still no good.

When the Glow plugs are out you need to ream out the carbon build up. There is a special reamer for that or there is alternative methods like using a drill bit turned by hand. The end of the reamer is 7mm.

Repair Links

Fast navigation http://www.peachparts.com/shopforum/diy-links-parts-category/146034-fast-navigation-do-yourself-links.html

You can't test the earlier individual filament/loop type glow plugs on the battery as it quickly buns up the filament.
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1984 300CD, won't start in coldish temps.-glow-plug-test-bad-2019.jpg  
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  #13  
Old 01-31-2019, 10:05 AM
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How to use starting fluid/either in an emergency.

Go to the Glow Plug Relay and unplug one of the electrical connectors. That keeps your glow plugs from coming on and igniting the starting fluid prematurely.

You are going to avoid using too much starting fluid by having someone else crank the Engine while you spray as little starter fluid as is needed into the Air Filter Housing (remove the inlet tubing that is in front of the Air Filter Housing).

If you spray a large amount of starting fluid into the Air Filter Housing and then run, get inside of your Car and attempt to start you risk getting a large slug of Starting Fluid into the Engine. When that happens is want makes damage more possible.

Not disconnecting the Glow Plug connector also increases the chance of Damage.

If the intake is short I have seen people start Diesels with WD-40. That won't work if the distance from where you are spraying to the Cylinder head is long.

In an extreme extreme emergency I have seen my Boss soak a Rage in Gasoline and stretch a single ply of the Cloth across the intake opening (on a Truck). He wrapped his hands around it so the Rag on the end of the manifold so it would not be pulled in and had me crank the Engine. It started.

Story time: I have been sent out on 2 separate jobs where it turned out the Diesel Engine would not start even with Starting Fluid. Both engines were direct injection engine with no Glow Plugs or other cold weather starting system (this is in southern CA).

In both cases the compression was too low to start.

One was a loader like a large fork lift that was worked 24 hours a day. As long as it kept running there was no issue. But, someone ran it out of fuel and it sat unused for 12 hours.

The other one was a 3 cylinder ford tractor (like a farmers tractor) that sat in a rental yard for extended periods. Since the Port of Long Beach is a few miles away it is likely that if it sat long enough unused the rings got stuck.

In both cases the Company Mechanics did not diagnose the issue correctly and sent the Fuel Injection Pumps to us t be rebuilt. I had to go to their places of businesses because they thought we had botched the fuel injection pump rebuild.
It seems pretty clear that if you are cranking the Engine and fuel is getting up to the Injectors that the only other issue could be if the Fuel Injection Pumps were timed wrong. And, I checked that and the timing was OK.

As part of the trouble shooting process I used the Starting Fluid/Either. If the Engine won't start on even attempt to start on the Starting Fluid you know there is something more seriously wrong.
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Last edited by Diesel911; 01-31-2019 at 10:16 AM.
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  #14  
Old 01-31-2019, 11:04 AM
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After you've got your glow plugs straight, here are other things you can do to increase the odds of a successful cold start.

- Adjust the valves. Tight valves decrease compression, making a cold start nearly impossible.

- Use synthetic oil, like Mobil 1. Much much better cold flow characteristics, allows starter to crank over the engine faster than regular non-synthetic oil. Simple to test this property, put a small sample of your oil and small sample of synthetic oil into your freezer overnight, and see how well they pour out the next day.

- Ensure the battery is fully charged, good clean connections at the battery and good cables (no corrosion) and good connection at starter motor and ground strap from engine to body of car.

- Glow the plugs - the light in the dash is simply a timer, the relay continues to power the plugs until the safety limit is hit (about 30 second or more), if your car is parked in a very quiet place you can hear a nice "thunk" from under the hood when the relay shuts off, that is your signal to turn the key to "start" and crank over the engine.

- Use the cold start procedure in the owner's manual (accelerator pedal held to the floor while cranking, don't release the key until engine RPM starts to increase so that it will continue to run without the starter motor).

- Block heater - use it if you've got one. They need about 30 minutes to an hour to work their magic, so you can set them on a timer if you don't want to leave the car plugged in all night.

Note that starter motors get tired and slow with age, so consider getting a fresh starter if you've still got issues.

Another trick would be bringing the battery indoors for the night, a warmer battery has more cranking power. Put it on a trickle charger. Battery warming mat (aka heat pad) can be placed under the battery to keep it toasty overnight, in the car. I think El Mercado del Wall sells them for about $15 in the pharmacy area.
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  #15  
Old 01-31-2019, 11:46 AM
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Post Cold Weather Starting Drills

All good points .

If you have the average old Mercedes Diesel OM616/617 it helps to wait for the seat belt lamp to go off, as mentioned this allows the glow plugs to warm fully as it's slightly longer than the glow plug relay's lamp in timing .

Of course, those valves really NEED periodic adjustment, a thing almost always neglected or ignored when it should be the very first thing done .

The starters are a PIA to remove but once off the car are easy to take apart, clean, maybe solder on new brushes and grease and re install for faster cranking and more years of perfect operation .

Mind the battery cables are squeaky clean too ! .

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