Magnetic Drain Plug?

[kid-jensen]

Anyone know the thread size on the front and rear Diffs of my 2007 ML W164)

I'm looking for a magnetic drain plug but the suppliers need to know the size first..

 

[optimusprime]

Contact other makers they will know ,you could just stick magnets on the case .

 

[optimusprime]

Paul looking on mb forum a member on there purchased a number of sump plugs from Mercedes Drilled them 1/4 in the centres and glued in the magnets he had off ebay on to the 2 bottom drain plugs .

 

[kid-jensen]

I had considered that but I've also heard a few snags...

1. Most magnets loose a lot of their magnetic attraction at high temperatures (some times nearly all of it), this would result in them letting go of all the iron/steel shavings which would then wash around with the oil, just as before. Worse than that, you wouldn't know this was happening!

2. I'm sure the axle gets hot enough to degrade most glues. I seem to remember Araldite is not much use above 100C..

I guess it's up to me to research the upper working temperatures of the Magnet and epoxy before I buy.

Good luck with that on ebay!

 

[markjay]

Had a magnet in my Vauxhall sump plug for many years with no issues.

It was a round thingy shaped like a very thick coin, and was hanging on to the metal plug on its own steam (or magnet) - no adhesive used.

I don't do DYI servicing any more so longer bother with it.

 

[hotrodder]

I had considered that but I've also heard a few snags...

1. Most magnets loose a lot of their magnetic attraction at high temperatures (some times nearly all of it), this would result in them letting go of all the iron/steel shavings which would then wash around with the oil, just as before. Worse than that, you wouldn't know this was happening!

2. I'm sure the axle gets hot enough to degrade most glues. I seem to remember Araldite is not much use above 100C..

I guess it's up to me to research the upper working temperatures of the Magnet and epoxy before I buy.

Good luck with that on ebay!

Diff oil isn't gonna get hot enough to worry any of the common flavours of magnet. A neodyium (NdFeB) is as good as it gets upto ~150°C, above that an SmCo magnet outperforms it and continues to past the NdFeB magnets max recommended temp of 200+ all the upto 300ish °C. Curie temps are way, way higher.

The usual DIY flavours of Araldite (rapid, precision etc) are rated to a max of 65°C which maybe* isn't quite good enough... diff oil is rarely gonna reach let alone exceed 100°C (60 maybe 70 upto 90ish usual running temps?) and if temps go much over 120°C for any lenggth of time the magnet or the glue holding it to the plug will be the least of your problems
Araldite make epoxy adhesives with far higher max temps, 2014-1 for example is rated to 120°C, but like other high temp adhesives from Loctite etc the price goes up significantly for a small tube of the stuff i.e. if no one can/will tell you the thread size it'd probably be cheaper to buy new plugs from MB, measure 'em throw 'em away and then buy the magnetic variety
Have a look at oven door glue (high temp silicone based adhesive) if you want to stick a magnet to your existing drain plugs and/or can't be without the car for a few days while waiting for the new magnetic plugs to arrive. Temp ratings will be more than high enough and it'll be cheaper

* it's not like it'll fail the moment it reaches 65°C, like you say it degrades so as temp goes up strength and other properties fall. At what point it'll be unable to keep a small magnet stuck to a bolt while it's subject to some vibration and temp cycling i don't know

 

[kid-jensen]

Hotrodder,

Great information, thanks.

Looks like the most practical way-out is to buy a new drain plug from the dealer and measure it.

I've never been to a Merc dealer in all the years I've owned Mercedes, should be an educational experience for me...

 

[kid-jensen]

Just to put this to bed, I took the easy option and drilled a new drain plug and epoxied a neodyium magnet in it (3 x 10mm).

It's now in position and I'm sure doing what magnets do. If it only extends the life of the Diff by a couple of years, it'll be worth it.

As is my experience in the past, the oil change made no difference to the whine I get at certain speeds. I didn't expect it to, but the magnet certainly eases my concience....

I had to buy a dozen of thse neodyium magnets, and I was thinking of offering the spare ones to anyone that asked, but as they were 99p for a dozen, including postage, that doesn't make econiomic sense!