Last summer (2009) I bought several sets of aluminum valve stem caps from Harbor Freight. My old plastic valve stem caps were falling apart, these looked good, and the price was right. They included a nice knurl on the outside and a rubber seal at the inside end. When I put them on I did notice that they were a little long, but they still seated all the way.

Fast forward to spring (2010). When I went to check the tire pressures on my wife's daily driver, a Dodge Caravan that sees lots of road salt in the winter, three of the four valve stem caps were firmly corroded in place. I tried pliers, only to have the rubber valve stems rotate in the wheel! I applied PB Blaster daily for about a week and tried again; still no luck. I finally had to carefully cut the damned caps off the valve stems with a Dremel tool. Upon inspection, the one cap that came off normally appears to be 100% anodized ... inside and out ... while the other three (the ones I had to cut off) were only anodized on the outside; the inside threads were bare aluminum.

My conclusion? It is probably best to avoid this product altogether, especially if your car is ever exposed to salt (either winter or seashore). It is possible that applying a small amount of dielectric grease or anti-seize to the valve stem threads would have prevented the corrosion, but I'm not willing to experiment to find out. In the future, I will use only brass, plastic, or passivated stainless steel valve stem caps, and with any metal cap I will use anti-seize.

One bright note. These valve stem caps sealed really well. The tires on my wife's Caravan lost less than 1 psi between Christmas and April ... an all-time record for our cars. This means to me that brass caps with rubber seals in the end are probably a good idea.

[This message has been edited by Marvin McInnis (edited 08-26-2010).]

No plus for you, only one per member allowed, .
I will give you a , an atta-boy, and a pat on the back.
Thanks.

This could have ended badly for someone without your removeal skills, costing someone more then a few bucks.

Great warning post.
Thanx.

Ya i was actually looking at a set for the Fiero to match the wheels. I think ill pass too

A bit of dielectric gel will keep them from anodizing. I do not have the harbor freight ones, but mine are also aluminum. I have had a similar experience on another vehicle years ago. The dielectric gel provides a barrier between the aluminum and the valve stem.


Yes, antisieze works too. I imagine that wheel bearing grease would work, but have never tried it. The antisieze is just dirty.

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[This message has been edited by Tony Kania (edited 08-26-2010).]

u experienced the problem that makes the wings fall off airplanes no really im serious, what u have going on is a chemical reaction between two dissimilar metals creating a battery like effect,(hydrogen embrittlment is one of the results) it is usually present where the fillet panel meets the wing root wich is titanium and between it and the landing gear mounting bits, then they top it off by using steel cherry max rivits! anyway the aluminum corrodes all to hell in those spots and in some cases is a major repair along with other areas hawker 700 800 900"s also have metal to aluminum problems with the rivits in the wings and the only solution is replacment or sand blasting them and then covering them with carboline wich brings me to my next statment f u want to use steel with aluminum put a good layer of carboline between them it will protect them also on somthin like a wheel cap die eletric greese is good teflon tape on the threads with the die eletric grease is better water wont wick past the threads then!

[This message has been edited by jetsnvettes2000 (edited 08-26-2010).]

Same thing happened to a co-worker's vehicle with factory caps. The shop couldn't get them off, so they just replaced the valve stems. I had stainless steel caps on my Grand Prix and never had a problem (even with winter salt).

quote Originally posted by jetsnvettes2000: u experienced the problem that makes the wings fall off airplanes no really im serious, what u have going on is a chemical reaction between two dissimilar metals creating a battery like effect...

Yep. Try a Google search for "galvanic corrosion" if you're interested in the technical details.

I wouldn't just say the Harbor Freight caps, I'd imagine this could happen with any aluminum cap.

im willing to bet you could have held the valve stem with a pliers, and turned off the cap with another pliers
i find it hard to believe that they really "needed" to be cut off

sorry im not a hater, just seems like there was an easier solution

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AIM:Onefast2M8
00 VW GTi VR6 -- Not stock
06 VW GTi 2.0t

Thanks for the initial warning post, and the informative replies. Never hurts to lube!

quote Originally posted by jetsnvettes2000: ... what u have going on is a chemical reaction between two dissimilar metals creating a battery like effect ...

I'm quite familiar with galvanic corrosion. A hard anodized (i.e. passivated) surface on aluminum is in itself a good electrical insulator. It is, after all, a thin film of Alumina (aluminum oxide) ... the same Al₂O₃ that's used for spark plug insulators. If only the threads of the valve stem caps had been properly anodized they might not have corroded. As I mentioned earlier, the threads of the fourth cap (the only one that didn't seize in place) seemed to be anodized the same as the exterior surface.

Concerning aircraft, if you want to see a real corrosion nightmare try attaching bare aluminum to carbon fiber using plain steel fasteners, without any insulating barriers. It won't take long to see results.

quote Originally posted by $Rich$: im willing to bet you could have held the valve stem with a pliers, and turned off the cap with another pliers i find it hard to believe that they really "needed" to be cut off

I tried that on all three, without success. There's a fine line between gripping the rubber base of the valve stem "firmly" and damaging it, and if I erred it was on the side of caution. Even after I had slit one side of the caps with the Dremel, they still didn't want to come off until I had used a flat-blade screwdriver to spread them open slightly. They were really solidly corroded on there. I'll try to post pictures later.

[This message has been edited by Marvin McInnis (edited 08-26-2010).]

quote Originally posted by Blacktree: Yep. Try a Google search for "galvanic corrosion" if you're interested in the technical details.

Yep. Galvanic corrosion is a common problem with boat engines, especially those which see salt water. Boat motors use a dissimilar metal which acts as a preventative.
Dang, ... now I am gonna have to Google.

quote Originally posted by cliffw: Anode was the word which escaped me.

Sacrificial Anode. On my boat outdrive, the trim tab was the sacrificial anode.

quote Originally posted by FieroRumor: Never hurts to lube!

So, KY could work?

I kid, but nice job on the reporting - something like that would match my wheels nicely but I'm good with plastics.

quote Originally posted by litespd: Sacrificial Anode.

The zinc galvanizing on steel parts is one of the most common forms of sacrificial anode. The zinc will slowly be consumed as it protects the steel from rust and corrosion. Once the zinc coating is gone, the steel will begin to rust.

Cadmium is another material that acts as a sacrificial anode and is used to protect steel parts. It is even more effective than zinc in most applications, but cadmium usage has decreased in recent years due to it's relatively high toxicity.

The magnesium rod that's installed in your home hot water heater (or at least the rod that used to be there before it dissolved) is another form of sacrificial anode. Some cars used to have sacrificial blocks of zinc or magnesium dangling in the coolant just below the radiator fill neck as a corrosion inhibitor.

[This message has been edited by Marvin McInnis (edited 08-27-2010).]

i have the same valve caps on my car too. i do have aluminum cz rims on my car, when i clean my rims, i do put anti-seeze on where alum. touches the hub and lugs too. i am going to do my valve caps too. i donot drive my car much, never in the rain, if can help it.plus i do check my air pressure often. i do have alum. valve caps w/ plastic inserts, thay are on my motorcycle.