3 dead glow plugs in 1 day??? - Page 2 - PeachParts Mercedes-Benz Forum

layback40 · #16 09-19-2010, 10:20 PM

911,
I think when you have a carbon build up & the motor is up to temp. Any of that carbon that starts to glow or burn as it will on a good hard run, will weaken the surface of the GP that it is near & so lead to premature GP failure.
The increased high current time you mention increases the internal temp of the GP and can cause them to burst open & so cause a stuck GP.

tangofox007 · #17 09-19-2010, 10:20 PM

Quote:

Originally Posted by sixto

Yup. The that vintage glow relay cuts when you hit the starter. Why would you want to stop the glow cycle before hitting the starter?

Actually, the cycle ends when you release the key from the start position.

sixto · #18 09-19-2010, 11:03 PM

Quote:

Originally Posted by tangofox007

Actually, the cycle ends when you release the key from the start position.

You need to glow longer if you know that

Sixto
87 300D

funola · #19 09-19-2010, 11:54 PM

"Current hogging", "hogging caused by a cascade " in a glow plug ??? Never heard of it before. Care to explain?

Quote:

Originally Posted by wgilmore

Another interesting glow plug story, like mine where I had a hard to start issue and all glow plugs checked fine and then the next day 2 checked bad.
I think this may be an issue of current hogging... .
I can't explain why 2 of my glow plugs failed at the same time actually, but since it is a parallel circuit, I vote for hogging caused by a cascade .
I just replaced them all and hope they last a few years.
The hogging is common in semiconductors with a low dynamic resistance and can cause this sort of thing to occur without proper safeguards.

funola · #20 09-19-2010, 11:57 PM

Quote:

Originally Posted by Diesel911

I agree with vstech.

The manual also has that a bad Injector Spray pattern can cause early Glow Plug Failure.

What brand were the Glow Plugs that Failed.

You can make your own Reamer from one of the no good Glow Plugs. In the DIY section somewhere.

They are all used Bosch glow plugs. Mechanically they look fine, no stripped threads, no tip erosions etc.

How would a bad injector spray pattern casue early glow plug failure?

funola · #21 09-20-2010, 12:18 AM

4 out of 5 glow plugs were difficult to remove! They didn't want to come out even totall unthreaded due to carbon holding it back. What cause carbon to form in the prechamber? It is a dead-headed cavity with no combustion flow through it. You'd think the red hot glow plug would burn whatever carbon gets in there and keep the area clear. Is it due to poor injector spray pattern? injection timing off? Anyway I had to pry the glow plugs with long nose pliers as I turn the glow plug with a gear wrench to get them out. I happen to have a glow plug reamer I made (7 mm dril bit + old glow plug) and it came to good use. It took a long time to ream out all 5 holes as I had to apply forward pressure with one hand while I turn the reamer with a gear wrench with other hand in an awkward position. Wheel bearing grease on the reamer helped it stick to the carbon.

I'll be checking out the glow plug controller next to see if it is misbehaving.

Diesel911 · #22 09-21-2010, 02:09 AM

On my 84 the Glow Plugs get Voltage while the Engine is Cranking.

On the Termial Block infront of the Battery in the most forward part of the Terminal Block is a one White Wire (that comes up from the Starter Solenoid) and a Purple Wire (that goes to the Glow Plug Relay) are screwed together on the Terminal Block.

When you Crank the current comes up from the Starter Solenoid by way of the white Wire and into the Purple Wire and on to the Glow Plug Relay.

I am guessing it is done that way so that if a person is lazy to use the Glow Plug Light and just jumps in the Car and starts it if he/she cranks long enough the Voltage to the Glow Plugs will also heat them and aid in starting. The Glow Plugs working during cranking must be way better than just cranking alone during starting.

layback40 · #23 09-21-2010, 05:18 AM

I suspect that carbon build up is also related to how the car is used. Our diesels when ever used always get a run for at least 15 minutes at 60mph. We never see carbon build up. If you are mainly using yours for around town trips mainly stuck in traffic, st a couple of miles do to the shop& back, expect problems with things claging up.

MBeige · #24 09-21-2010, 11:45 AM

Quote:

Originally Posted by vstech

yeah, the relay is loud clicking on and off, but once you've started the car I challenge you to hear the click

With the doors and windows closed you will still hear it faintly from inside the cabin, if you listen hard enough.

That said, I wouldn't put used glow plugs in my car.

funola · #25 09-21-2010, 10:13 PM

Quote:

Originally Posted by MBeige

With the doors and windows closed you will still hear it faintly from inside the cabin, if you listen hard enough.

That said, I wouldn't put used glow plugs in my car.

Why not? It's not a critical mechanical part and there is little risk. The worst that can happen is they burn out. I have been using used glow plugs for 20 years and run them till they burn up and put another used one in. It's rare that I bought 5 new glow plugs a few weeks ago (as an experiment to see how long new ones will last). If they burn up in less than a year I am going back to used plugs.

Edit: Forgot to mention when I pulled the old glow plugs, I checked each one again with an ohm meter and this time only 2 plugs are bad. I am certain I did not make a mistake the first time when I found 3 were open. I think it was just a case of an old intermittent glow plug.