How To Change Glow Plugs
 

I usually never have a topic because i use the (HELPFUL) search tools. However i could not find exactly what i need on "how to change glow plugs.

Here is the story. About 5 days ago my glow plug illumination would sometimes not come on and the car would still start. Yesterday it (my 86 300sdl) did not start and the glow plug lamp is not lighting. I came to the conclusion that it has to be my glow plugs. I've also called around and the mechanic said most likely that what it is (glow plugs). He also said it will be $300 to replace. I've changed spark plugs many times (in American cars) but i have never changed glow plugs. Is this something i can do myself or should i let it be done by a mechanic? and would i have to change all the plugs?

the plugs are $10 piece and i don't want to spend an extra $240 for something i can do myself.

In this forum (diesel) it's the second thread DIY - scroll down to Glow Plug Replacement.

dmon,

Before U replace something that moght not be broken, do a resistance test on the GP. It is unlikely that more than one GP goes bad at one time.

It may just be the fuse strip in the GP relay. They have been known to get a crack in them and not work. It could also be a bad GP relay.

P E H

Test them first. Disconnect the plug at the GP relay, use a multimeter, measure ohms to chassis ground of each plug.

GOOD = 1.1 ohms down to 0.8 ohms or so.
BAD = open (infinity, flashing digits, etc.) or 0.0 ohms (shorted internally)

Note which GP(s) are bad, should be two or more for lamp not to light.

Numbers on plug, and diagram on relay box, will tell you which cylinder number goes with which wire.

If they all test GOOD, check sockets and corresponding pins on relay box for corrision, clean it all off, and see if lamp now lights. I had corrosion on 2 pins, GPs were GOOD, corrosion blocked current so GP could not work. Cleaned the pins, and all is well.



Remove and replace GPs confirmed as BAD.

10mm wrench or socket to remove the wire from the GP. On OM603 the nut is captive on the wire, others be prepared for nut to leave the wire and hide...

An assortment extensions, and universal joints, etc. will allow a 12mm deep socket on the plug for removal like a spark plug. I like 1/4" drive, easier to thread through the obstacles.

A special reamer can/should be used to chase the carbon from the threads, but is not be absolutely necessary. Anti-seize on new GP threads before reinstalling won't hurt, either.

Install, 'medium' hand-tight, 'snug' torque. Replace wire, snug.

There are a lot of other threads on testing and replacing, may be harder to find. Others will post links soon, I bet.

Best Regards,
Jim

thanks.

i'm going to try these after work. by the way could glow plugs effect my instrument cluster lights?

dmon,

Only way I know how GP would affect instruments lights would be when energizing the GP, the instrument lights and any other lights will dim slightly. This normal and is caused my the approximately 70 amp current draw of the GP.

P E H

If you do need to change your glow plugs, you might find it useful to remove the intake to perform the task. While I know it can be done with the intake on, I figured it would be easier to just remove the intake. Of course I have a habit of breaking things when I need to work at awkward angles in tight spaces. Also a good time to clean the sludge out of the crossover pipe and intake.

how not to break the wire?
 

How do you remove the nut holding the wire onto the glowplug, without the wire twisting, and usually cracking right at the crimping spot? I tried jamming a screwdriver in there while turning the nut, but still some movement, and so I think I "cracked" 3 out of 4 of the wires leading to the plugs. There is electrical continuity, and the engine starts fine, but I hate the thought of having stressed the wires unnecessarily.

very good info.
this would also apply to my 1986 300sdl right?

yeah i need to know that too. i work better with pictures.

Also a tip, you could call it, is that I know when I change my plugs it isnt the easiest to get them completely unscrewed with the wrench. What I did was go down to the Home Depot with a glow plug and found a nice rubber hose that fits snuggly over the gp. When I get the plug cracked with the wrench, I put the hose around it, its about 8" or so and turn the hose. Makes the one behind the IP very easy to get out.

Breaking News
 

BREAKING NEWS
i think i found out the problem. as was suggested i checked my gp relay and the silver fuse strip is cracked. i will replace today. after i replace the strip should i still consider changing my glow plugs or all should be well.

Thanks

I would still test the GPs with a meter. If you find one (or more) shorted GPs (0.0 ohms) you have found the reason that the fuse melted, and it will melt again.

I won't recomment replace a GP unless it tests BAD. (and neither will P.E.H.) :D

Best Regards,
Jim

Best Advise Yet...
 

If you start to change them out...
Put a large towel folded up into the space between the IP and the Block...
every little thing you drop goes right into that abyss.....

dmon,

If the fuse was cracked instead of melted you don't have a shorted GP and none should have to be replaced.

But while you are working there, do a resistance check of the GP. If all read 0.6 to 1.0 ohms, the GP are all OK.You need a digital ohmeter to get good readings.

If you don't have a digital meter, get one. They can be bought for ~$20, less than that set of GP you wanted to buy. But I would suggest a better one at ~$30 to $40. Still less than the GP you don't have to buy.

P E H