Three problems related to tire valve have been reported for the 1998 Ford F-150. The most recently reported issues are listed below.
I have had 2 valve stem, break causing the tire pressure to decrease. About 3-4 months apart.
This is for defective valve stems. I purchased new tires from mavis tire corp. In November 2006 and in June 2008 I had 1 valve stem fail. It happened while the car was parked. I brought it back and had to insist to have it replaced free of charge since it was a defective part. At that time I did not know of the problem that existed with the stems. Now I am beginning to wonder if the other 3 valve stems will fail as well. I am sure they will not replace them free of charge without a recall.
Purchased 4 new tires approximately June 2006 from ntb. One year later had blow-out and purchased new tire. Shortly thereafter had 3 flat tires and ntb said that the valve stems were defective and replaced. I believe that the blow-out that I had was a result of a defective valve stem, but there was no way to prove.