Which sealant to use?
 

I've been told that when I put my engine back together, that I should use the MB sealent. I heard this referred to as either blue or black. Which is it? Is there a part number?

Some time ago I was tolk the MB Blue sealant was actually made by Hylamar, which can be bought over the counter.

i believe that most of these OEM sealants are really permutations of Permatex variants. permatex's OEM black sealant equivalent is called "The Right Stuff". i associate blue ones with the older RTV sealants which you have to be careful with as they can mess up o2 sensors (there are o2 sensor approved versions)...

The correct sealant from Mercedes is a black color and actually mentions something about 'radiator' on the label. However, it is the correct sealant for the covers. Expensive I think, like $20 for a tube. Comes in a large hyperdermic (without needel) looking configuration.:)

The sealant that MB dealers are supposed to use is Loctite 5900, MB part number 002-989-73-20-10. IT is a special black silicone sealant. List price is $15.

MBDOC,
That's very interesting information! Loctite sells this stuff in europe but not here in the US where they only sell glues and thread lockers for retail. They also sold the Permatex business to Permatex! I wonder if Loctite 5900 is actually Permatex's Right Stuff in US markets (you can get this at Pep Boys) because it is used for the same applications...

ps. and you could save 3 bucks - the Permatex stuff ain't cheap either :(

There are several DIFFERENT sealants. Each has it's use. What part of the engine are you talking about?

Just as you don't use the same lubricant for engine, a/t, power steering, rear axle, etc., you don't use the same sealant for every part of the engine.

Have a great day,

Michael, a couple of tips you may want to consider; Make sure both surfaces are clean by wiping with denatured alcohol.
and
Apply a narrow, well rounded bead of sealant and do not flatten out over the surface before assembly. This ensures not using too much and still maintaining good contact on both surfaces upon tightening.

I use the OE sealant that MB DOC is talking about only. It is good for almost every cover and mating surface on the engine.
This sealant is the best I have ever used. It is very strong and durable.

Don't ever use any sealant on Head Gaskets!

from what i saw at loctite.com, the applications are everywhere you might get leaks - timing chain cover, valve cover gasket, oil and tranny pan etc. etc. etc. BTW i'm reading my canister of permatex right stuff and it says "copyright of loctite corporation". the MB/loctite sealant dries to a black rubbery compound right?

I have assembled several engines using permatex/loctite/napa sealers and the last two engines using the MB stuff. The MB stuff is expensive but it seems to be much better than anything else I have ever used. All the engines assembled with the MB approved sealant are bone dry - the permatex assembled engines "weep" a little bit. I suspect Larry Bible is correct - its important to make sure you have the correct sealant for the job but the MB stuff seems to work everywhere I have tried it.

How much is it worth to you to have a leak free engine ?? $20 seems pretty cheap.

Thanks for all the feedback. I surely won't skimp when it comes to sealant. I'll use whatever is best for the job.

Larry,

Is there anything you would not use the black MB sealant for?

There is one place that the black sealant should not be used.

Where two plates seal together to form a passage for oil or fuel. (like in the inside of the front lower timing cover and in the inside of the rear main seal cover)

In this case, I use the MB sealant all around the outside and I use a Hylomar type sealant on the oil pressure passages. It is available through the Wurth company and it is the Green sealant. On all front lower and rear covers, I do it this way because I have seen a small piece of rubber silicone break free and cause cam bearing failure in the V-8's.

Take it from me, adhere to this advise and you will have a leak-free engine and a piece of mind.

Michael,

Benzmac has more experience with the sealers than I, but I would share one thing regarding your M103 motor.

I have had good success with the upper timing cover of the M103 by using the blue translucent MB sealer. It has an acetone type smell rather than an acetic acid smell like most silicone sealers. The reason I use this sealer on the upper timing cover is that it will allow the lower U shaped gasket to stay in place while sliding the cover rearward over the shaft seal.

Benzmac may have experience with the black stuff over this seal working as good or better. I use the blue stuff because it has never failed for me. If the black stuff they're talking about is like the "right stuff" that I've used before, it would seem that it would be too tacky to allow the cover to slide over the seal without moving it. These guys experience with the black stuff for this application may prove okay for this application.

I had an old pickup that had an oil leak at the point where the oil pan met the timing cover. It was a pretty significant leak. I took a finger full of the "right stuff" and crammed it into the area of the leak, let it set over night and it never leaked another drop ever again. Amazing stuff!

Good luck with your rebuild,

The only sealant(engine & drivetrain) approved by MBUSA for warranty work is LOCTITE 5900. ON "all" surfaces & applications!!
AS Benzmac said YOU must be careful around oil passages not to use "TOO" much! Have seen several damaged camshafts from other shops after doing a rear main seal & using excessive sealant! THIS sealant started out as industrial only and now EVERY new MB engine uses this on almost every surface "INSTEAD" of gaskets.

Answers my question!