OM606 glow plug removal tips and tricks
Back on 12 March l finally had to change the glow plugs on my ’95 E300 Diesel, with OM606.910 (non-turbo) engine. At least one was bad (I only measured the resistance of #1 through #5) and the pre-glow timer light would never light during starting but would always light immediately after starting, and cold starts were very rough.
I spent a couple of weeks reading everything I could on this forum and asking fellow MB diesel owners what the secrets are, and now I will share them with you, as well as my experience. Using the steps below, I successfully removed all six plugs that were very much stuck and carbon packed and just begging to be broken off by an impatient, unaware and unprepared mechanic.
This job took me over nine hours from start until all the new plugs were in. I’m in a holding pattern right now, as I had to order some parts from dealership. Hat tip to Greazzer (
http://www.peachparts.com/shopforum/members/greazzer.html), I sent the injectors to be rebuilt with new nozzles and he turned them around in 24 hours and I had them back in hand on the fourth day after I mailed them to him (helps that I’m in Charleston SC and he’s just up the road a couple hours). Thanks for that great service!
Here are the key tips and tricks:
1. Hot engine. Drive the car until the engine is hot (I drove my car for about 45 minutes, performing a few Italian tune-ups, AC blasting on full, to get that engine nice and hot), and then plug in the block heater as soon as you park in the work area. Hotter is better. The block heater kept the engine temp up over 80 deg C for quite awhile, and I think it only dropped down to about 60 deg C by the end of the ordeal, about nine hours later. Ambient temps were about 70 – 75 deg F.
Is it a good idea to start the engine during the process, between plugs, to keep the temperature up? Maybe, maybe not. Consider that at idle, more carbon may be deposited in the pre-chamber and on the plugs, so that may work against you. You would also need to leave the injectors installed.
2. Liberal use of penetrating oil. I used PB Blaster – it was what I had. Immediately after the intake manifold is off, begin applying that oil. I had ordered some Kano Aero Kroil, but it didn’t arrive in time.
3. Use a torque wrench for removal set to 40 or 45 Nm, gently work them back and forth to slowly work them out. The Beru glow plug literature says that 45 Nm is the maximum torque specified for removing the OM606 glow plugs (12mm threads). Can one use more force? I did a destructive test on two old Beru star-marked plugs (MB dealer parts), and found one broke at 74 Nm and the next at 81 Nm, using MY torque wrench, which may or may not be calibrated. Stick with 45 Nm on YOUR wrench, unless you have a couple plugs to destroy to “calibrate” the breaking torque of your plugs on your wrench. Some have reported plugs breaking off at much lower torque values. Are Bosch or other brands weaker? Good question, I couldn’t find any data to support that, but there are reports of the Bosch plugs rounding off easily. The faces of the hex portion are bigger on the Beru plugs. Unlike in the OM616/617/601/602/603 engines, Beru seems to have a better reputation than Bosch plugs in the OM606.
4. Remove the injectors and apply penetrating oil to the inside of the plugs! The first two plugs came out with much effort, over about three hours, and the rest either would not move or moved very little (I did not try #6 yet at this point, I decided to leave it until the end because access is blocked by the oil filter canister and I wanted to make sure I did not break off that plug). I decided to remove the injectors and apply penetrating oil inside the pre-chambers to loosen the carbon on the inside. This helped! Every thirty minutes or so, I refreshed the penetrating oil both inside and out for all the remaining old plugs, using over half a can of PB Blaster during the job. I made a spray tube extension with an angle at the end to direct the spray to the side of the pre-chamber with the glow plug. I used an old piece of plastic vacuum tubing, heated with a propane torch until it was just soft and I could make a nice bend, and then cut off the tube just past the bend.
Result: the #6 plug had about six hours of soaking with PB Blaster. It was amazing how easily it came out. It came out SO much easier than all the rest. I should have STARTED the job by removing the injectors and spraying the penetrating oil inside the pre-chambers as well as outside. I highly recommend this if you run into the least bit of trouble getting the plugs to move. Note that you WILL need to change the engine oil after contaminating it with the penetrating oil and all the carbon that you wash out of the pre-chamber.
The blow-by-blow description of the job…
I was able to remove the intake manifold in about 20 minutes. I started with the glow plug that presented easiest access, #5, using a 12mm deep well socket and a torque wrench set at 30 Nm. I had only applied penetrating oil to the outside portions of each plug. My engine harness was replaced with a new dealer harness about five years ago, but I had a LOT of trouble getting the connectors to pop off the glow plug terminals. Only one or two came off by hand, the rest required that I lever them off from the back side, using a tool meant for pulling interior paneling plastic pins / rivets. The tool has a flat face that is forked, so I could fit that around the glow plug pin and apply pressure to a good bit of the surface of the electrical connector. Very strange! I will apply some dielectric grease during assembly this time.
First up: Plug #5. Very gently applying force to slowly creep up on the torque setting of 30 Nm, the plug would only turn a couple of degrees. After the first turn CCW, I turned it back CW, and then repeated. After going back and forth a few times, the plug seemed to be getting tighter! Yikes! Danger Danger! When any nut or bolt gets tighter as you work it back and forth, it is a BAD sign, and the risk of breaking something goes up. If this happens, stop, take a break, apply more penetrating oil, try a different plug, keep your cool and be patient. Strangely, after leaving that plug alone for just ten or fifteen minutes, it was looser when I went back to it. I continued on with the CCW and CW bit, slowly getting more movement in the CCW direction, until the plug started tightening up again! I took another break, came back and found it loose again. I’m not sure what was going on here, but patience and gentle persuasion were the order of the day and those two qualities served me well.
#2 was the second plug I worked on, and it was moving about like #5. #4 didn’t seem to want to move at all, neither #3. I tried #1, and had it moving gently back and forth, when as I was tightening it back in a little… “CRACK!” and the wrench jumped. I was convinced I had broken the plug, and my heart sank. I removed the wrench, cursed a bit. I regretted not making some phone calls during the work week to see if any local shops had the special tool set for drilling out a broken plug. I sent emails to my MB buddies lamenting my woe. Applied sack cloth and ashes. Said a prayer that I wouldn’t break any more plugs.
I went back to #5 and #2, and slowly I was able to get all the threaded portions out, limiting myself to just 30 Nm. This took about three hours. Once the threaded portions of the plugs were out, more penetrating oil and grab the plugs with vice grips and twist and pull, twist and pull, until both plugs were out. Both were Beru star-marked. The inner body of each plug, the last 0.5 to 0.75 inches, was black with soot. Obviously the plugs had not fully seated and carbon was able to pack in around the body.
I decided to measure the resistance of #1, to see if the filament was broken; maybe I could leave it in place until later? It measured about 1 ohm, which is good. I decided to see how completely broken it was to see if it might hold together for a bit, and to my surprise it was NOT broken and indeed was still very tight and stuck. Oh happy day! However, it would not move at all with 30 Nm of force.
I went back to #4. The Beru guide offers that applying 12v to heat the plug for 3 or 4 minutes might help to loosen it, so I tried that. 3 minutes of current using a jumper cable from the battery positive, but that didn’t help at all.
Time for plan B!
At this point I did the destructive testing referenced above, and thenceforth I used 45 Nm as the maximum torque for removing the remaining plugs. I also decided to remove all the injectors and soak the inside ends of each plug with penetrating oil. I had thought of this method earlier but never heard of anyone else trying it. Can’t hurt, right! I think it made a big difference, and I recommend it.
The remaining plugs went a bit faster, but it was still slow patient back-n-forth. I found that once I had the plug turning in the CCW direction without reaching the 45 Nm limit, it was best to just keep loosening the plug, as going CW a bit was liable to increase the amount of force required to loosen again. Almost all of the plugs came out with a crack-crack-crack as the carbon bound them up. Once I had them most of the way out on the threads, I would soak outside again and then turn the plug all the way back in, hit the inside end with penetrating oil and then bring the plug back out until the thread were free, hit the inside again with penetrating oil and then start the twist and pull. The restricted access plugs were not easy, I used a pair of line-man’s pliers to grab the notch at the end of the plug, lever against the edge of the head above the plug, while twisting the plug with a box-end wrench.
The last plug was #6, trapped behind the oil filter housing. I had to loosen the engine harness plastic support at that end and move it up a bit to get as much room as possible. To my happy surprise, that plug came out with minimal force. Soaking the inside (pre-chamber) end of the plug for about six hours with penetrating oil made the key difference, I think. #6 showed the same carbon packing on the body as the rest of the plugs, and none had any hint of never-seize.
Breaking Torque Values gleaned from comments in the various posts: “Mark in MA” measured the torque needed on an old glow plug to break it between threads and hex at about 80-90Nm.
“Pimpernell” read that the breaking point of the plugs is in the range of 40-45 Nm. (Beru literature says 45 Nm).
“Notfarnow” broke one off at ~40Nm. Beru from dealer with starmark. [Ed: was his torque wrench out of calibration? 40 Ft lbs set instead of Nm?]
TimFreeh did a little destructive testing with old glow plugs: Beru branded OEM plugs. Holding the glowplug in vice supported on the case of the plug (the area between the threads and the heating element) the head of the glow plug will shear off at 85-90NM.
Replacement / Installation
1. Ream the carbon out of the holes.
2. Apply anti-seize to the glow plug body and threads.
3. Torque to 22 Nm or 25 Nm. The FSM says nothing about applying anti-seize to the plug body or threads, and lists 22 Nm as the torque. Beru advises to coat the plugs with their anti-seize, and lists 25 Nm torque. Some advise going a little higher, 27 Nm, to ensure that the plug shoulder seats well and blocks carbon from building up inside the head and packing in the body of the plug.
Tools and materials
6 Beru glow plugs
1 intake manifold gasket
~1.2 meters of injector return line hose
6 injector heat shields
[Optional: plastic clips and rubber shims for the fuel lines; rubber and plastic piping for the crank-case breather tube “octopus”; O-rings for all those pesky fuel line connections; new copper crush washers, O-rings and springs for rebuilding the delivery valves “while you are there”.]
Penetrating oil
Anti-seize. I found a Permetex brand aluminum based product at AutoZone which is rated to stand up to 1600 deg F.
“Special Tools”
12mm deep well socket.
Torque wrench that includes range of 20 – 70 Nm (I have two wrenches to cover this).
Special socket for the injectors.
Hazet 4760-1 glow plug swivel socket (from Peach Parts) allows access to the plugs with restricted access: #1, #3, and #6.
Glow plug hole reamer
“Regular Tools”
5mm hex
?? Torx (intake manifold screws)
10mm socket
Vice Grips
Lineman’s pliers
Wire brush