Glow plug failure - interesting point to ponder?
 

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?

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.

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!

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.

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.

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

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

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 ...

It does not even take 30minutes to figure out which one is bad and R&R it on an OM617.

I have about a dozen or so used glow plugs (from the junkyards) that I just swap out whenever one goes bad. When I get a rough idle on a cold start, I know one is bad and i replace it.

Glow Plugs
 

This gets me thinking about a glow plug amperage sensor for each plug that would indicate current draw for the individual plugs....It could be a homeade device with needle or LED indicators...under dash mount or such.....It would tell you how much current each plug draws....would not have to be very large and would tell you which plugs to replace as needed....The relay sort of does this with the magnetic reed switch sensing total current draw to light the glow plug lamp...just a thought...there may already be such an animal....

or you could take five minutes to pop the harness connector and test them with an ohm meter. :)

Len

I always pull mine and bench test them. Yes it takes a little longer but then there is never a doubt. I've heard of people who had their plugs test fine with an ohm meter but failed the bench test.

Scott

Ohm test....
 

That is the problem I ran into....good ohms check and failure at operating temps....An ohmeter cannot begin to duplicate the current and resistance changes that happen in a plug under power...As the plug heats up resistance changes pretty drastically.....your looking at maybe 50 amps of glow current ....an ohmeter cannot get anywhere near that.....It is ok for a quick check and is correct for most cases but can be misleading ......High current devices can drive a dedicated ohmmeter user crazy...It has happened to me many times....and will probably get me again...I may be stupid ...but at least I am slow.....

When you guys refer to bench testing, I assume you mean sticking it in a vise and hokking it up to see if it glows and stays glowing? Perhaps this idea of a plug checking good but failing as it heats is my issue as well, still fighting that blinking light going down the road, but it always happens after the engine has begun to show warming on the temp gauge. Still trying to understand why it gets to blinking several minutes after the glow cycle has long passed as well, I know the relay is not sticking on and that the contacts arent welded shut for a fact from prior testing. Can the plugs be removed and reinstalled if a person does not have a reamer handy? (My only hesitation to pulling them)
-Chris

Reaming the hole is kind of a luxury option. it's not necessary when you change a plug.

I've had all 5 of mine in and out at least three times each without issues.