Glow plug failure - interesting point to ponder? - PeachParts Mercedes-Benz Forum

stephenson · #1 12-31-2006, 01:41 PM

Another quick glow plug story ....

My light stopped illuminating about 6 months ago (but, would illuminate about 30-60 seconds following startup) ... with roughness at startup ... was generally warm weather, but I knew cold was coming ... rougher and rougher as the weather cooled. From all the great posts here, it appeared this was a common phenom.

So, quickly did the standard continuity check from the battery to the harness plug at the GP relay - only number 5 was showing completely open, so dug out set I removed four years ago ... they all tested good. Removed and tested #5 (easier than I thought it would be, but no all looked as easy), and it was open. Replaced with one of the old ones (all Bosch, btw, but new ones had a slightly different design with tapered end) and works great - start up much smoother!

Now, to the "point to ponder" - it appears from my reading here that most folks simply replace all the GPs when they tackle the job (several folks have mentioned having 3 or 4 GPs inop, but don't mention the GP light not illuminating - non-loop, perhaps?) ... perhaps a more reasonable course of action is to replace only the ones that are bad vice the entire set? This premise based on thought that some GPs have a production flaw that causes them to short or open during use and some GPs may never fail ... comments?

Matt L · #2 12-31-2006, 02:04 PM

They will all fail eventually, but you're not wasting any time doing them individually on the older engines. If you have one bad one and they're all several years old, I'd do the whole batch anyway.

Bodgit2 · #3 12-31-2006, 02:11 PM

I think cleaning out the hole with a reamer and never seezing all of them is a good idea. I'd replace them all to save labor when the next one dies. We use them more up here than you cause it's cold here!

STIX240D · #4 12-31-2006, 02:11 PM

I recently went through GP nitemare. Replaced a few a year ago and presumed they were good. Finally decided to check them, and 4 of 5 were dead, 2 of which were replaced a year ago.

The one good one was a German Bosch, Im almost sure, never been replaced in 26yrs. I replaced the other 4, with after market, because I needed to use car today, but next replacement will be BOSCH.

My lite always came on, not too familiar with how it works exactly, I think the old GP's were wired in series? so if one went out lite did not come on. Mine are wired in parallel so if one dies the lite still comes on.

However, now I come to think of it, before I chaned the glowplugs, the lite came on solid, then after a few minutes started blinking, now it starts blinking right off.

Anyone? Comments??? Thanks.

nhdoc · #5 12-31-2006, 03:16 PM

Blinking means there's a problem. The light is supposed to come on, then after a period of time (2-30 seconds) go out and stay out until the next time you start the car. Any behavior other than that means there's something wrong, most likely a GP or several are burned out.

Jadavis · #6 12-31-2006, 03:56 PM

The main reason I replaced all of mine was because I have the 603 engine and had the intake manifold out anyway. They are not as easy to get at on the 603.

-Jim

toomany MBZ · #7 12-31-2006, 06:28 PM

Just replace the faulty ones. However, I have a full set, just in case.

stephenson · #8 01-01-2007, 01:04 AM

Not sure everyone is getting my point ... perhaps some GPs are going to fail simply because of production quality - i.e. once you replace the bad ones, you will get very long life.

If you replace all at the same time you end up in the same boat - with a mix of ones that are going to fail and ones that will last a long time ... again, replacing the ones that fail with ones that haven't (something you won't know until you remove them after long life) will ensure a set of long life GPs ...

mespe · #9 01-02-2007, 10:24 AM

My experience tells me that GP's may fail intermittently, meaning you cna ohm them out, but after they start to heat up they open. My car went through a period where she ate GP's. I replaced the one's I had with store bought Motor craft GP's which really suck. Thank God the Ford plugs have a 2 year warranty. I also believe that when a GP fails, the others are stressed more (higher voltage due to the remaining GP's which shortens their lives)

Replace the one that's burned out to buy you time. Then replace all of them , saving the old ones for a cold rainy day.

Mustang_man298 · #10 01-02-2007, 09:59 PM

Well, looks like I might have to play the plug pulling game this weekend then, I have 4 spares from my old engine, one original MB (has the star on it) and 3 fairly clean and fresh looking bosch. This will be interesting to see how it turns out. Of course, this will be if I have time after the tractor gets fixed, had that one apart for 2 yrs now

, FINALLY got past the hurdle I've been beating my head on (with help from cold weather), got all the remaining parts I needed today, so this weekend it's on! I'm bound and determined to get that spot on my shop floor back so I dont have to grade the driveway by hand anymore....and get my better half to stop reminding me daily of it...

...All I wanted to do to it was fix the brakes....then the trans went out...DOH!

mobetta · #11 08-26-2008, 08:19 PM

as I understand it, it seems to be a perfectly operational system.

the relay will get a signal from the ignition switch when you start the car(search violet wire mod) which will then shut off the plugs. if you do not start the car, the plugs stay on, but the "wait to start "light will go off sooner or later, depending on temps.

your right on the the 2 sensors- one is for the gauge on the dash, the other for the GP system.