Mercedes ML CDI Glowpulgs

[craig511]

Hello all ,

Is there any benefit to replacing all 6 glow plugs on my Merc ?

I want to give it a service but the cost of plugs alone would be £120 ish .

Are they like spark plugs in that they degrade over time or do they either just work or not ?

Cheers

[anonymous-user]

Does the symbol in the dash display go out and stay out after you start the car? If it does then they're all ok, and personally I'd leave them alone.
If the symbol comes on again, and stays on for a minute or so, then one or more of them has packed up. The easy way to find out is to take the car to a decent indy and get the diagnostics plugged in, which will indicate which of them need replacing.
Or, if you've got a multimeter, check each plug for resistance (there should be some, I can't remember how much) If any of them show no resistance, then they are the duff ones.

[anonymous-user]

Glow plugs are not like spark plugs at all.

Avoid touching them unless the car wont start in the cold. They are a different construction to a spark plug and are notorious for snapping in the head, they are then a right pain to get out. I had all sorts of issues on a Discovery with some and ended up spending hundreds getting them professionally drilled out.

[TBSC]

I agree with not touching them if there are not faulty. I had a CLK 270 that had the fault that showed up as the pre heat light coming back on after starting and the garage managed to snap one of the plugs off and ended taking the head off to get the remains of the plug out. Good job it was under warranty.

[philcray]

As above, I had a 2003 ML270cdi from new for 175k miles, the glow plug light would stay on for about 5 minutes after setting off, seemed to have no adverse effect and was advised to leave alone.

[Blackpuddin]

I've got this issue with my W124 E300TE, two of the glowplugs are faulty. She still starts, albeit lumpily for the first 20secs, then all is good. My local garage is trying to pluck up the courage to take on the job of replacing them but I wouldn't be surprised if they knock me back as by all accounts the only way to sort it is to snap the electrodes off, carefully drill out the rest of the plugs and use a slide hammer to rip them out. The normal method of slathering them with releasing fluid for a few days and/or applying heat doesn't work. Dieselpump UK put a video up on YT about it. Unfortunately they don't offer this as an outside service. I may have to leave it as it is and keep my fingers crossed.