One year old bad glow plug - Page 2 - PeachParts Mercedes-Benz Forum

Biodiesel300TD · #16 02-21-2011, 08:39 PM

Quote:

Originally Posted by layback40

This is the best piece of advice on GP's in the thread.

I agree.

Do you think he lit his cigarette with the GP when he was done?

Skid Row Joe · #17 02-21-2011, 09:34 PM

Quote:

Originally Posted by Diesel911

The Glow Plug in the far left pic is not a good one because it is getting hottest at the wrong place on Element. That no good plug may actually Ohm OK.
The other pic on the right is a good Glow Plug getting hottest at the tip of the element. The tip is the part that extends into the Precombustion Chamber.

I appreciate the instruction, Diesel 911. Thanks!

Diesel911 · #18 02-22-2011, 12:03 AM

Quote:

Originally Posted by spark3542

I figured my statement would trigger this response, but I still stand by it. Perhaps heat areas do not stay optimum throughout the life of the GP, but 99% of GP-related questions on the forum are a go/no go issue. If you're reading megohms, your GP is bad, if you're reading an ohm, there's 144 amps going through that plug on a 12v system. Ohm's law holds...If there's 144 amps going through your GP, it's turning into heat. No other option.

The Fuse is 80 amps. I would expect the Fuse to burn long before it reaches 144 amps.

Also the Glow Plug in my picture that is heating mainly in the middle could case a miss on that particular Cylinder because the Heat would be trying to heat up the Cylinder Head and the Coolant (because that is what surrounds the Glow Plug in that area of the Plug) instead of heating the Air in the Prechamber.
Even though the Glow Plug has only partially failed it may functionally mimic a dead Glow Plug.

Diesel911 · #19 02-22-2011, 12:09 AM

Quote:

Originally Posted by Biodiesel300TD

I agree.

Do you think he lit his cigarette with the GP when he was done?

No, I did not light a Cigarette with it.
I smoked a Pipe back in the early 1970s for 2 years (Tobacco only) after which I lost interest in smoking.
But, like past President Clinton "I did not inhale".

whunter · #20 02-22-2011, 02:27 AM

Quote:

Originally Posted by JayK

I had the classic signs of a bad glow plug.
* No pre glow light.
* Rough starts.

I ohm-ed the connector leading to the plugs, and saw 2.6 MΩ on #3.

With the cross pipe off, and #3 disconnected.
I measured the plug directly and see 2.6 MΩ to ground.
So definitely a bad plug.
Luckily, I can reach it without taking the intake manifold off.

My question is, what's the chances of the plug breaking after being in the car just one year?
Are they weak from the get go, or does it take time?
The top end was rebuilt and clean as a whistle when the new plugs were installed; I don't know if that makes a difference.
Also, should I try to take it out cold, or with the engine warmed up?

Thanks.

Best guess the glow plug should still come out fairly easy.

****************************
NOTE:
Some of our customers that where forced to remove the head due to stuck/broken glow plugs, remove them every year to ream the hole, clean and lubricate the threads.
***************************

While diagnosing the glow plug system, do NOT touch any part of a hot glow plug.

Glow plugs run 1000° - 1300°C = "2372° Fahrenheit" optimal temperature range.

Touching the glow plug wire nut can cause severe burns, especially if there is a fault causing it to overheat.

Trying to OHM a heating element designed for high temperature operation at ambient temperature gives a deceptive reading.

A new glow plug reads 0.7 OHM.

Heating the air to a minimum starting temperature of 850°C is critical for diesel engine start-up.

FYI:
The most common (good quality) "NEW" glow plug failure is over torquing the 8 MM wire nut = damaging the electrode internally.
This is an ELECTRICAL connection = watch the wire, and STOP tightening when it begins to move.

All of this being said, I junk any glow plug reading 0.9 or higher.
For best reading:
* Disconnect the glow plug harness from the relay.
* Red OHM meter wire goes on the 8 MM wire nut threaded pole/terminal.
* Black OHM meter wire goes on the steel body of the glow plug.

All of my used glow plugs are tested:
# With the HOT electrode in the jaws of a vice.
# Battery/charger ground attached to the vice.
# Positive applied to the wire nut threaded pole/terminal for 15 seconds.
After you have tested one good glow plug, and personally seen how bright/hot it gets, there is no mistaking weak/bad ones.

Please read the data in the following thread for further data.

Glow plugs link thread All diesel models
http://www.peachparts.com/shopforum/diesel-discussion/137732-glow-plugs-link-thread.html#post1019018

.

spark3542 · #21 02-22-2011, 08:06 AM

Quote:

Originally Posted by Diesel911

The Fuse is 80 amps. I would expect the Fuse to burn long before it reaches 144 amps.

It was a math exercise. If the fuse is 80a, then the resistance of the glow plug has to be more than 2.178 ohms (if the battery is at 13.2v) to not blow the fuse. I'm not makin' this stuff up...Ohm's law holds everywhere.

funola · #22 02-22-2011, 08:51 AM

Quote:

Originally Posted by spark3542

It was a math exercise. If the fuse is 80a, then the resistance of the glowplug has to be more than 2.178 ohms (if the battery is at 13.2v) to not blow the fuse. I'm not makin' this stuff up...Ohm's law holds everywhere.

Huh???

funola · #23 02-22-2011, 10:03 AM

Quote:

Originally Posted by spark3542

I figured my statement would trigger this response, but I still stand by it. Perhaps heat areas do not stay optimum throughout the life of the GP, but 99% of GP-related questions on the forum are a go/no go issue. If you're reading megohms, your GP is bad, if you're reading an ohm, there's 144 amps going through that plug on a 12v system. Ohm's law holds...If there's 144 amps going through your GP, it's turning into heat. No other option.

Do you have a weak battery in your calculator perhaps because those numbers are way off!

funola · #24 02-22-2011, 10:12 AM

Quote:

Originally Posted by Diesel911

The Glow Plug in the far left pic is not a good one because it is getting hottest at the wrong place on Element. That no good plug may actually Ohm OK.
The other pic on the right is a good Glow Plug getting hottest at the tip of the element. The tip is the part that extends into the Precombustion Chamber.

The glow plug on the right is either not powered up long enough or is not getting full current. I have never tested a glow plug with just the tip glowing. Unless all the glow plugs I have tested were no good?

whunter · #25 02-22-2011, 11:06 AM

Quote:

Originally Posted by funola

The glow plug on the right is either not powered up long enough or is not getting full current.
I have never tested a glow plug with just the tip glowing.
Unless all the glow plugs I have tested were no good?

Pictures.

Never Touch Hot Diesel Glow Plugs!!!
http://www.peachparts.com/shopforum/diesel-discussion/134359-never-touch-hot-diesel-glow-plugs.html#post986836

NOTE:
I always keep one "NEW" glow plug in my tool box for demonstration/comparison testing.

funola · #26 02-22-2011, 11:20 AM

Glow plug on the right been powered for 2 seconds. By 20 seconds the entire shaft (up to the bevel seal) should be glowing.

http://www.peachparts.com/shopforum/attachments/diesel-discussion/28981d1129501651-never-touch-hot-diesel-glow-plugs-a1.jpg

spark3542 · #27 02-22-2011, 12:24 PM

Quote:

Originally Posted by funola

Do you have a weak battery in your calculator perhaps because those numbers are way off!

Yup, sorry bout that...I had watts on the brain when I typed amps. The concept is still there...resistance determines the amps, amps determine the heat generated.

Diesel911 · #28 02-22-2011, 12:28 PM

Quote:

Originally Posted by funola

The glow plug on the right is either not powered up long enough or is not getting full current. I have never tested a glow plug with just the tip glowing. Unless all the glow plugs I have tested were no good?

It is a Monark not a Bosch glow Plug. And, it might be that I took the pic too soon. However, the point is that Heat strated at the tip and got hottest their first.

Diesel911 · #29 02-22-2011, 12:34 PM

Quote:

Originally Posted by spark3542

Yup, sorry bout that...I had watts on the brain when I typed amps. The concept is still there...resistance determines the amps, amps determine the heat generated.

When I tested some Glow Plugs one at time with an Amp Meter the Meter pegged out and as the Glow Plug heated up the Amps dropped to around 16 amps and stayed there.
It only took about 2 seconds for the Amps to drop to 16 amps.

Quirky Mercy · #30 02-22-2011, 09:52 PM

What is the best type of GP to use? I installed 3 new Bosch and it starts worse. I am going to put the old GP's in. I think they are Beru?