Valve Stem Caps
12-02-2007, 12:08 PM
#1
Intermediate
Thread Starter
Member Since: Jul 2007
Location: Catonsville MD
Posts: 26
Likes: 0
Received 0 Likes
on
0 Posts
Valve Stem Caps
As the guy at the tire shop was patching my run-flat, he said that the valve stem covers should be aluminum or plastic. He said that my chromed steel ones aren't compatible with the tire sensors.
I've never heard of this nor can I find any reference to this on the Internet. Any credence to his comment?
I've never heard of this nor can I find any reference to this on the Internet. Any credence to his comment?
12-02-2007, 12:14 PM
#4
Race Director
Member Since: Jan 2005
Location: Bay Shore, NY 11706 MILD2WILD (M2W)
Posts: 13,656
Likes: 0
Received 7 Likes
on
5 Posts
St. Jude Donor '06-'07
As the guy at the tire shop was patching my run-flat, he said that the valve stem covers should be aluminum or plastic. He said that my chromed steel ones aren't compatible with the tire sensors.
I've never heard of this nor can I find any reference to this on the Internet. Any credence to his comment?
I've never heard of this nor can I find any reference to this on the Internet. Any credence to his comment?
12-02-2007, 12:15 PM
#5
Safety Car
Member Since: Dec 2004
Location: Tucson AZ
Posts: 4,276
Likes: 0
Received 8 Likes
on
4 Posts
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
There is a reference in the owners manual - or at least in my 05 manual. Basically, the stock cap works/acts as an antenna for the sensors.
I have never had a problem with "steel" caps.
12-02-2007, 12:25 PM
#8
Race Director
Dissimilar metal corrosion is one issue. The main thing to be concerned with here is to make sure they use nickel plated valve stem cores, not the brass ones that are used in a lot of other applications.
The main reason they say to run aluminum or plastic caps is because the valve stem is part of the antenna circuit for the sensor. The sensor manufacturers say this, and then, of course, the car manufacturers and tire shops pass on this info as a CYA thing.
Butt....a number of forum members have cut off the valve stem when mounting the sensors inside the wheel with bands or straps in some aftermarket wheels that don't accept them in the valve stem hole as in an OE wheel. Most have not had any major problems with the valve stem removed - the sensors still seem to transmit okay, but probably not with quite as strong of a signal.
So....whether it's for corrosion reasons or due to messing up the signal strength of the transmission from the sensor, don't worry about it. I've been running chrome caps for 2-1/2 years on my '05 with no problems at all.
Bob
Forum member formerly known as "beezeye"
The main reason they say to run aluminum or plastic caps is because the valve stem is part of the antenna circuit for the sensor. The sensor manufacturers say this, and then, of course, the car manufacturers and tire shops pass on this info as a CYA thing.
Butt....a number of forum members have cut off the valve stem when mounting the sensors inside the wheel with bands or straps in some aftermarket wheels that don't accept them in the valve stem hole as in an OE wheel. Most have not had any major problems with the valve stem removed - the sensors still seem to transmit okay, but probably not with quite as strong of a signal.
So....whether it's for corrosion reasons or due to messing up the signal strength of the transmission from the sensor, don't worry about it. I've been running chrome caps for 2-1/2 years on my '05 with no problems at all.
Bob
Forum member formerly known as "beezeye"
12-02-2007, 01:43 PM
#9
Race Director
Quote from my '05 Service Manual; ''the cap is aluminum and the valve is nickel plated to prevent corrosion and are not to be substituted with a cap or valve made of any other material". Page 3-93, 4th paragraph.
12-02-2007, 01:49 PM
#11
Racer
Member Since: Jul 2007
Location: Crab Orchard Tennessee
Posts: 317
Likes: 0
Received 0 Likes
on
0 Posts
12-03-2007, 07:02 AM
#12
Team Owner
In the case of Chrome plated caps, they will actually reduce the potential for galvanic corrosion as they are closer together on the table (as long as the chrome plating on the threads holds up) once it fails then the base metal comes in to play. The elements at the top half of the table are more active (anodic) the elements at the bottom of the table are more passive (cathodic).
Galvanic corrosion is the corrosion that results when two dissimilar metals with different potentials are placed in electrical contact in an electrolyte.
A difference in electrical potential exists between the different metals and serves as the driving force for electrical current flow through the corrodant or electrolyte. This current results in corrosion of one of the metals. The larger the potential difference, the greater the probability of galvanic corrosion.
Galvanic corrosion only causes deterioration of one of the metals. The less resistant, active metal becomes the anodic corrosion site. The stronger, more noble metal is cathodic and protected.
Galvanic corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly. Metals close to one another on the chart generally do not have a strong effect on one another, but the farther apart any two metals are separated, the stronger the corroding effect on the one higher in the table.
This table lists the potential differences for various metals in water. The order of the series can change for different electrolytes (for example, different pH, ions in solution).
I have omitted Stainless steel alloys from this table as they can significantly change their potential and become much more active if exposed to stagnant or poorly aerated water.
A difference in electrical potential exists between the different metals and serves as the driving force for electrical current flow through the corrodant or electrolyte. This current results in corrosion of one of the metals. The larger the potential difference, the greater the probability of galvanic corrosion.
Galvanic corrosion only causes deterioration of one of the metals. The less resistant, active metal becomes the anodic corrosion site. The stronger, more noble metal is cathodic and protected.
Galvanic corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly. Metals close to one another on the chart generally do not have a strong effect on one another, but the farther apart any two metals are separated, the stronger the corroding effect on the one higher in the table.
This table lists the potential differences for various metals in water. The order of the series can change for different electrolytes (for example, different pH, ions in solution).
I have omitted Stainless steel alloys from this table as they can significantly change their potential and become much more active if exposed to stagnant or poorly aerated water.
Electrode Potential at 77 F (25 C)
Anodic end (this is where the corrosion occurs)
Element Standard Electrode Potential (Volts)
Lithium -3.045
Potassium -2.920
Sodium -2.712
Magnesium -2.340
Beryllium -1.700
Aluminum -1.670
Manganese -1.050
Zinc -0.762
Chromium -0.744
Iron; Mild Steel -0.440
Cadmium -0.402
Yellow Brass -0.350
50-50 Tin-Lead Solder -0.325
Cobalt -0.277
Nickel -0.250
Tin -0.136
Lead -0.126
Hydrogen reference electrode 0.000
Titanium +0.055
Copper +0.340
Mercury +0.789
Silver +0.799
Carbon +0.810
Platinum +1.200
Gold +1.420
Graphite +2.250
12-03-2007, 07:53 AM
#14
Drifting
12-03-2007, 08:21 AM
#15
Melting Slicks
Member Since: Jun 2007
Location: San Antonio TX
Posts: 2,241
Likes: 0
Received 0 Likes
on
0 Posts
Just a sidebar before this gets ugly 
, if you're using the nice C6 emblem plastic caps, periodically check to make sure the little O-rings stay in place. They have a tendency to come loose and lodge themselves in the neck of the valve and not allow air in.
BTW...Talon90...YOU DA MAN!
, if you're using the nice C6 emblem plastic caps, periodically check to make sure the little O-rings stay in place. They have a tendency to come loose and lodge themselves in the neck of the valve and not allow air in.BTW...Talon90...YOU DA MAN!
12-03-2007, 09:03 AM
#16
Team Owner
02-13-2008, 11:14 AM
#17
Racer
Member Since: Aug 2007
Location: Plain City Utah
Posts: 378
Likes: 0
Received 0 Likes
on
0 Posts
02-13-2008, 11:21 AM
#18
02-13-2008, 11:40 AM
#20
CF Senior Member
Member Since: Feb 2006
Location: Tucson Arizona
Posts: 23,313
Likes: 0
Received 19 Likes
on
18 Posts
BEZ06 is the resident expert when it comes to tire pressure sensors. His instructional videos on TPMS tools are an invaluable resource for all forum members...he knows what he's talking about!
talon90...thanks for providing such complete information. Just because someone prefers the "Readers Digest' version don't let it bother you. The over-whelming majority of forum members value your expertise and the information you provide to educate us all. Your time and efforts are greatly appreciated.
talon90...thanks for providing such complete information. Just because someone prefers the "Readers Digest' version don't let it bother you. The over-whelming majority of forum members value your expertise and the information you provide to educate us all. Your time and efforts are greatly appreciated.