Mercedes Aftermarket Valve Cap Issue
 

A notice that the "metal" Mercedes valve caps may cause serious issues.

I'm not sure if I should have used "anti seize" or the recent hot weather expanded the metals and made the stem and cap super, super tight but 3 of my 4 valve stems are now ruined which are part of the TPMS sensors and expensive to replace.

I installed the caps last year and didn't have any problems as I do check my tire pressure every 1-2 months. Last time I checked my pressure in April when I put my summer wheels back on I had to mar a few of the caps as they were very tight and a vise grip was needed. I figured the tires were stored all winter and the excessive sit time of metal to metal was the cause of metal bonding. I assumed the tires are back on for the summer and the caps will be off on a regular basis for pressure checks again so no need to worry. My mistake as this past weekend (only 2 months later) the caps were frozen on to the stems.

1) As I tried to get one of the caps off it "broke" half my valve stem threads off with it exposing the inner part of the schrader valve.
2) Another cap froze on and ruined the valve stem threads as I removed it.
3) One stem is fine.
4) The 4th stem was frozen as well and I just left it for now.

Are the aftermarket caps brass coated or aluminum? If brass coated they bonded to the Aluminum of TPMS sensor.

Metal caps....
 

...can also interfere with the proper functioning of the TPMS...

That is crazy. I bought the plastic caps and my wonderful dealership told me I should use the metal caps instead. I just switched back to my plastic caps.

Oooo no metal...
 

I would like to hear a technical explanation of this claim.

BTW, I've had the metal caps on my car since 10/07 with no problems of any kind.

Um, just so no one gets confused ... here in Seattle, the average temperature is something like 60 (or lower), so there's very few days where we get high temps that could cause anything like metal expansion ....

Brass adhesion may differ .....

For my part, I already made a note to stay with the plastic OEM stuff.

Too heavy anyhow...
 

I bought a set of the aftermarket caps and just felt they were way to heavy and stuck out way too far...glad I took em back.

The corrosion (or metal bonding) creates a weakened valve stem. I've seen it time and again with cars with TPMS systems and traditional metal valve caps (unless they are aluminum). They stem itself is cracked from some sort of undue stress typically creating a leak at the stem itself.

There have even been numerous problems with aluminum caps becoming useless and quite brittle just from age. The aluminum cap is so extremely thin that it just doesn't hold up to any sort of weathering very much. As such it is best with a TPMS equipped vehicle to simply run the traditional black (or any color) plastic valve caps.

I will have to scrape the chrome plating off and confirm but I bought the OEM caps if that helps.

As a few people have mentioned the caps did "metal bond" to the valve stems.

I did a search on ebay and one seller is listing the caps as OEM but says they are "ABS plastic and chrome plated" I'm not sure if there was a change made as I do have the heavier metal ones of some type or the listing is wrong.

I'll contact Mercedes and see what they say and update this thread once I know more.

I have used a set of MB Accessory AMG chrome caps on three different cars and not had any problem in removing them. I have never really checked to see if they are ABS or aluminum but they have caused me no trouble.

No close-up available but you can see the cap okay.

http://nevadajack.zenfolio.com/img/v5/p150343130-4.jpg

I have almost the same identical caps on my car, I purchased them at the dealership and mine have the star logo on the end, I have never experienced any problem with them?
They just look better on the AMG wheel option than a black plastic cap?:y

Mine came with a silver plastic cap which looks much better than the black cap IMO.

Okay after having to deal with "stuck" metal aftermarket caps for the past year where I was always nervous about them not coming off ..... thus why I checked my tire pressure like every other week just to twist the caps occasionally ..... hhehe funny cause it finally caused me to check my pressure on a regular basis :)

Anyways I've been using the same fugly silver rubber caps and really want the nice MB logo caps but does anyone know if they sell these in rubber or in any kind of material that won't cause corrosion and get the caps stuck ??

It really isn't worth snapping a TPMS valve and replacing it just to have the nice logos I must admit but I'm pretty picky so I'd prefer anything better than the caps now :nix:

Sorry for the rant and long post :p:

If anyone wants, I'll sell my metal MB caps. Used them for about a year, but my new wheels don't have a front air stem (it's inside the inner barrel) so don't need them anymore. I've never had issues with sticking and don't check my air regularly lol.

I went to Merchant tire in November to have a tire patched. During the process they lost my valve cap and replaced it with a metal one. I have been out of town till a few weeks ago. I was checking the tire pressure and noticed the brass cap that was fused to my valve stem. I went back to the tire dealer and they agreed to replace the TPMS after a short discussion. The cap Merchant Tire used was a brass cap.

It is odd the unforseen circumstances that come up with new technology. I never gave caps/valve stems a second thought before!

Beside caps/stems getting fused, be careful of them falling off also! I have had the opposite problem of the caps freezing. I bought the AMG plastic caps for my 18" AMG wheels. One cap apparently fell off after one day and the second one was damaged at the car wash, probably from the track the tires run through. they seem to stick out a little past the wheel. I have never had a cap fall off of my wheels before nor have any of my other cars ever incurred wheel or cap damage at this carwash. I don't want to keep buying $18 valve caps sets at the dealer, so I will revert to using the plain silver plastic ones that came with the car once all 4 AMG's are gone.

An Update.

I put my summer wheels back on last week where I had the one broken valve stem. While I was at Mercedes parts picking up a new sensor a service tech was in the room also and said "yeah you can't use the metal caps". I'm thinking to myself I get that now and that would have been nice to know before I broke a $105 part.

I'm not sure what year cars the metal caps are made for but they aren't compatible with new valve stems made out of aluminum. Why Mercedes continues to sell these is beyond me.