Last winter I got a wild hair and decided to put a set of “chrome” valve stem caps on my SAAB 9-5. Here is a photo of the one surviving chrome cap next to my current valve stem cap. I have no idea what material they were really made out of, they feel like maybe chromed aluminum.
I drove around all winter with those chrome caps, I even checked my tire pressure several times with no problems. Then one day in early spring I went to check the tire pressure and none of the caps would come off. I got one cap off with pliers, two came off with the help of two pliers working in opposite directions, the fourth cap wouldn’t come off no matter what I did. I chewed up the valves stem trying everything I could think of to get that last cap off.
I ended up taking the car to the local Kansasland Tire to have a new valve stem put on that wheel. I don’t know if they had to cut the old one off or what they did. I also had them rotate the tires while it was in the air.
What I noticed was the threads on the old valve stems were no longer brass colored, they were chrome. It appears that the chrome caps electroplated onto the brass stems. They all electroplated some, but that last stem & cap really bonded together. My best guess is the road salt and moisture next to the two types of metal was to blame.
So my advice is to avoid the cheap chrome valve stem caps.