I’m in Ohio where we use every form of ice melting compound known to man during our winters. Beet juice, rock salt, calcium chloride, salt brine, etc is used and it has vicious evil reactions, the worst being when you have galvanic electrolysis with dissimilar metals. Normally at work if we see aluminum valve stem caps they are removed and plastic ones go on to avoid the reaction with brass stems that makes them become one corroded mass. I have seen silver colored aluminum TPMS stems and we know not to put a brass core inside an aluminum stem because like most other dissimilar metals with a salt solution its a real no no. Seems like any forms of anti-seize hardly help when in this climate with winter road conditions.
Unfortunate for me, I didn’t realize my car had aluminum stems, being dark gray I never thought of it being a dark anodizing. They look almost black, I had removed a set of aluminum caps when I got the car and put on an old set of Audi logo chromed brass caps that I’d had on my older A4. That was 2 years ago, and I’ve checked tires about every 4-6 months. They looked great and I never expected any issues because in my head I’d eliminated the aluminum caps that cause most issues here. I never considered two other probabilities, that both would kick me in the ass.
Yesterday my low tire pressure light came on so I got out to check the tire. I was surprised when with my bare hand I twisted off the cap, along with it the end of the stem and the inner core. I put on my spare and headed home, sadly missing out attending an Octoberfest car rally between Zanesville and Athens Ohio. I was able to use a dremel tool to cut a slot in the other caps, then used a flat screw driver to twist and split the caps to get them off the other 3 wheels without major stem damage. There was some minor thread damage but they weren’t nearly as corroded as the one. I then observed that the one stem that crumbled in my hand had a brass core the rest all silver. I must have picked up the wrong one when I mounted the tires at work a couple of years ago. Now I’m waiting on 4 replacement TPMS stems and when I finish swapping them out I’m not only using just plastic caps but after I mount the tires I’m double checking that I haven’t picked up a stray brass core at the tire changing machine. I was shocked that even though I’d checked tire pressures many other times that they had just now seized the chrome caps to the aluminum, likely the salt from last winter resided in the threads enough to cause the damage. Even crazier since I’ve started to wash this car at least once every two weeks.
So with all the changes going on these days, brass stems , aluminum stems, chrome stems etc you can’t be so sure that even when trying to avoid mixing metals, shit happens. I’ve now got plastic caps on my both my cars and the snow tires to avoid ever having any kind of issue and I’ve now inspected all the cores to make sure I haven’t got any evil metal combination that would strand me. I was at least fortunate enough to have been gifted a spare full size Audi wheel with a new tire that someone had when they traded in a car with not just the space saver but two full-size extra tires. Service guys noticed one wheel matched mine. Its been gathering dust in my shed for a while, never thought I’d get to use it, crazy thing that karma.