Stainless steel valve caps and TPMS

[bmw1racer]

I wanted to replace the cheapie plastic valve stem covers on my wheels with the classic BMW OEM stainless steel valve caps, but I came upon this comment while searching:

"Wheel Valve Stem Cap Stainless Steel (4 Per Car) NOTE: Not for cars with Tire Pressure Monitoring System (TPMS)."

Any possible reason why?

[rps]

I've had them on my Z4 and transferred them to my 135 when I traded with no problems whatsoever.

[bmw1racer]

Maybe I need to submit this question to BMWNA.

[TMR013]

I would only be worried about getting them stolen.

[bmw1racer]

Originally Posted by TMR013

I would only be worried about getting them stolen.

Oh, I'm not talking about those fancy ones with the BMW logo on 'em, just the plain vanilla ones they used to use on BMWs:

[Qunadry]

The ones you refer to should not be used with the TPMS. The metal caps can cause the TPMS to malfunction. I bought the fancy Roundel caps for my 2012 135i and they could be used since they are plastic. They look the same as the steel Roundel caps I had on my 2000 323Ci. They also cost the same.

[bmw1racer]

Originally Posted by Qunadry

The ones you refer to should not be used with the TPMS. I bought the fancy Roundel caps for my 2012 135i and they could be used since they are plastic. They look the same as the steel Roundel caps I had on my 2000 323Ci. They also cost the same.

So the metal caps affect the TPMS somehow, huh?

Being a techogeek, now I'm curious how the TPMS works... Got any technical information on how it works?

[Qunadry]

Sorry I do not know how they work or why metal caps affect the TPMS but I was told this by several people who should know. BMW must have responded to people's desire for nicer caps by making the Roundel and M caps plastic.

[bmw1racer]

Ah, that's OK... I'll try Googling the subject... Thanks for the info.

[MadMan77]

I have had those run of the mill stainless steel caps on my 1er with TPMS for almost 4 years now. Never had a single problem so I am not sure what they could possibly do to damage the unit?

[jkoral]

Originally Posted by bmw1racer

Oh, I'm not talking about those fancy ones with the BMW logo on 'em, just the plain vanilla ones they used to use on BMWs:

Check out: http://www.bimmerfest.com/forums/sho...d.php?t=420856 (among others).

I had these on previous non-TPMS BMWs. Loved them so I put them on my non-BMW family car with TPMS (and aluminum valve stems) and learned an expensive lesson.

I've stuck with the plastic ones on my 135i.

[bmw1racer]

Originally Posted by MadMan77

I have had those run of the mill stainless steel caps on my 1er with TPMS for almost 4 years now. Never had a single problem so I am not sure what they could possibly do to damage the unit?

Still searching the 'net for info...

One thing I did read was that the valve stems are aluminum(?) and could chemically react (galvanic corrosion) with the steel valve caps, seizing the caps to the stems...

[bmw1racer]

Originally Posted by jkoral

Check out: http://www.bimmerfest.com/forums/sho...d.php?t=420856 (among others).

I had these on previous non-TPMS BMWs. Loved them so I put them on my non-BMW family car with TPMS (and aluminum valve stems) and learned an expensive lesson.

I've stuck with the plastic ones on my 135i.

Yup, I just read that...

Odd that the manufacturer of those TPMS sensors (Beru?) would use aluminum instead of the more typical brass.

[jkoral]

Originally Posted by jkoral

I've stuck with the plastic ones on my 135i.

Should be "stuck" (no pun intended)....



Also, @Qunadry, I've never heard of TPMS malfunction, only corrosion, leading to replacement of the more expensive TPMS valve stem. The TPMS continues to function but you can't put air in the tire when cap is fused to the vale stem.

[ken1137]

Ummm...the presence of an electrolyte and a electronic conducting path between the metals is essential for galvanic corrosion to occur. Thus, I believe it is basic corrosion. In addition, I believe the strange looking caps (w/the TPMS) indicate to any individual that a TPMS is present. Mine were stolen, go figure (?), so I have been using aluminum BMW logo caps.

OP...if it is 304 SS it will not corrode, but I guarantee it is not. I forgot to add; it is possible that a pool of water and salt can become trapped under the cap during the Winter if you are not careful. Then, you could have galvanic corrosion.

[bmw1racer]

Originally Posted by ken1137

Ummm...the presence of an electrolyte and a electronic conducting path between the metals is essential for galvanic corrosion to occur. Thus, I believe it is basic corrosion.

The electrolyte could just be water, which combined with the pollution in the air would create an acidic solution... Or maybe salt from the roads...?

In addition, I believe the strange looking caps (w/the TPMS) indicate to any individual that a TPMS is present. Mine were stolen, go figure (?), so I have been using aluminum BMW logo caps.

The caps on my car look like those cheapie black plastic ones painted gray... Guess I need to inspect them more closely.

[ken1137]

Originally Posted by bmw1racer

The electrolyte could just be water, which combined with the pollution in the air would create an acidic solution... Or maybe salt from the roads...?


The caps on my car look like those cheapie black plastic ones painted gray... Guess I need to inspect them more closely.

Yes, typically a salt or acidic solution but i think it is not likely if the caps have a good seal and you are careful. Then again SHIT happens

[bmw1racer]

Originally Posted by ken1137

Then again SHIT happens

Don't I know it...

[RPM90]

Originally Posted by bmw1racer

So the metal caps affect the TPMS somehow, huh?

Being a techogeek, now I'm curious how the TPMS works... Got any technical information on how it works?

Each wheel has a TPMS sensor that is attached to the valve stem. The sensor monitors the tire pressure using an internal pressure sensor. That information is sent via RF transmitter, which is part of the whole in-wheel TPMS sensor, that transmits it's "pressure data" to a centrally located receiver, which is located somewhere under the center tunnel below where the shifter is.

From the receiver there is a hard wire connection that feeds that data to the ECU. I found this out because that wire broke in my 135i.

The valve stem is part of the TPMS transmitter and may act like an "antenna", and if you use metal caps it may interfere with it's transmission.
But, as one poster has stated, his work fine.
So, there may be a potential for a problem, but it may work too.

Since you have them put them on and see what happens.
You can always take them off. Try installing 1 or 2 at a time and drive a bit to see if it affects anything.

BTW, if you're sure that your metal caps are stainless, then corrosion shouldn't be a big issue.
But, there is still a potential for the metal to somehow interfere with the TPMS transmission, IF that is the potential problem being warned about.

[RPM90]

Originally Posted by ken1137

Ummm...the presence of an electrolyte and a electronic conducting path between the metals is essential for galvanic corrosion to occur. Thus, I believe it is basic corrosion. In addition, I believe the strange looking caps (w/the TPMS) indicate to any individual that a TPMS is present. Mine were stolen, go figure (?), so I have been using aluminum BMW logo caps.

OP...if it is 304 SS it will not corrode, but I guarantee it is not. I forgot to add; it is possible that a pool of water and salt can become trapped under the cap during the Winter if you are not careful. Then, you could have galvanic corrosion.

Ah, now that may be why not to use metal caps, corrosion.

I had this happen in one of my cars years and years ago.
The wheels had the traditional brass stems, and I installed a set of aluminum anodized blue caps. Looked very nice on the blue car...kinda ricey.

Anyway, drove through the winter with water, salt, slush, and all manner of corrosive material picked up on the road.
In spring I went to check pressure and only 2 caps came off.
Those had serious corrosion building between the aluminum and brass.
The other 2 caps were LOCKED together as if fused by an arc welder.
Tried and tried to twist with hands, pliers, different pliers, different hands....NADA! Dremel tool to the rescue. I had to cut them in half to get them off, and did damage a bit of the valve thread. I cleaned them as well as I could and put rubber/vinyl caps on.

Stainless caps should work well I would think. I think I've seen a BMW set in stainless. They are semi shiny, but have a cool color that is not like polished steel or chrome. They have a softer sheen.

BTW, I've got a cool looking set of metal caps with the BMW roundel on the ends. They are made by BMW, and I don't think they are stainless, too bright and shiny.
I had them on my E46 325i.
I kept them before returning it for lease end. I took them off cause it felt like they affected the balance of the wheels/tires as I developed a very slight vibration at 55mph up. It was very slight, but I CAN NOT stand steering wheel vibe.
They feel quite heavy in hand, and I mean just holding one of them, you can feel the weight.

If I ever install them on my 335i Msport, I'll only do it when I can get the wheel/tire set balanced with the caps on.

[bmw1racer]

Originally Posted by RPM90

Each wheel has a TPMS sensor that is attached to the valve stem. The sensor monitors the tire pressure using an internal pressure sensor. That information is sent via RF transmitter, which is part of the whole in-wheel TPMS sensor, that transmits it's "pressure data" to a centrally located receiver, which is located somewhere under the center tunnel below where the shifter is.

From what I've Googled, I figured as much... Thanks.

From the receiver there is a hard wire connection that feeds that data to the ECU. I found this out because that wire broke in my 135i.

That's disconcerting.

The valve stem is part of the TPMS transmitter and may act like an "antenna", and if you use metal caps it may interfere with it's transmission.
But, as one poster has stated, his work fine.
So, there may be a potential for a problem, but it may work too.

Since the entire wheel is metal, I find it hard to believe that the little metal cap could have such a profound effect on the TPMS system... I think the corrosion angle seems more viable, but it's a guess...

Since you have them put them on and see what happens.
You can always take them off. Try installing 1 or 2 at a time and drive a bit to see if it affects anything.

BTW, if you're sure that your metal caps are stainless, then corrosion shouldn't be a big issue.
But, there is still a potential for the metal to somehow interfere with the TPMS transmission, IF that is the potential problem being warned about.

I think I'm going to leave well enough alone and not bother with changing the caps.

LOL, after browsing through eBay, some folks want $20 for a set of four of those plastic "TPMS safe" valve caps... Get real.

[F1Flagger]

Yes it is true. You should NOT use metal caps on TPMS systems. Corrosion WILL occur between the valve stem and the metal cap! Had it happen to my G-35 Coupe. Had to have the unit replaced.
You must use plastic caps