TPMS vale stem caps

[Reggaemon]

Whats the scoop with the TPMS valve stem caps?
On most cars they have a small metal cap. On my Subaru its
a normal looking plastic cap.
A mechanic at my tire place said I should change my metal caps to plastic. He said he has seen the metal caps get corrosion under them and cause problems with the TPMS.

Can or should I switch all my caps to plastic?

 

[Bill in Utah]

The only thing that the metal caps can do is *IF* you get corrosion that it *COULD* allow air to escape.

This could happen on TPMS or not equipped vehicles. Once you loose the air then the TPMS alerts you that the tire is low.

If you keep the caps on tight, you are fine. I would NOT replace them myself. Plastic or Metal does not matter IMB.

At work since 2006 all of our trucks (Toyota Tundra models) have TPMS. Not a SINGLE one works correctly.

We have had Toyota replace the units on the rims, reprogram the computer and after 4 years ALL the trucks have the light on the dash ALL the time.

And EVERYONE has plastic caps.

TPMS is another reason how to screw up something that is mandated. So the person just ignores the idiot light on the dash when in the beginning people should use common sense and CHECK the tires here and there.

Its another thing that I worry about *IF* I sell my 2007 Outback for a 2009/2010 Forestor. It would have the TPMS.

Take care, Bill

PS: What Subaru do you have? Any comments on it?

 

[stranger706]

I hate tpms. Its wreaked havoc on my mom's 07 Mini Cooper. It goes off all the time, and the tires are right at rec. pressure. The one time she hit a pot hole, and literally blew the tire out, the tpms never went off.

Another stupid law to cover up people's ignorance.

 

[Carbon]

You can use aluminum or plastic caps.

Do not use the classic brass caps, because they will corrode due to galvanic action.

 

[Bill in Utah]

Originally Posted By: stranger706
Another stupid law to cover up people's ignorance.

 

[Kestas]

I fail to see where brass caps cause galvanic action.

 

[Carbon]

Originally Posted By: Kestas
I fail to see where brass caps cause galvanic action.

The common RF TPMS uses aluminum valve stems. I don't know why they went to aluminum vs the classic brass. I suspect it was mainly cost. You don't see a lot of brass used in non-electrical hardware these days, since copper is expensive.

Maybe it was partially because many of the wheels are aluminum, although the valve stem's aluminum is not in actual contact with the rim; rubber is used between the metals to form the seal and resilient mounting. Maybe saving weight was a factor.

 

[Kestas]

Now I see. I didn't realize that the recent rise in metal prices affected valve stem materials. I imagine the TPMS uses more metal than regular valve stems.

I too doubt it's the aluminum wheels. The metals need to be in electrical (conductive) contact for electrolysis to occur.

 

[Carbon]

Originally Posted By: Kestas
Now I see. I didn't realize that the recent rise in metal prices affected valve stem materials. I imagine the TPMS uses more metal than regular valve stems.

I too doubt it's the aluminum wheels. The metals need to be in electrical (conductive) contact for electrolysis to occur.


The weight savings may have been a big factor, since the the TPMS is going to be a lot more to compensate for in balancing anyway.