My stock oil pressire gauge has been acting up a bit. I know i need to get a manual one. After driving for about 30 mins. the gauge sometimes goes into the low. It is still in the normal area but it conserned me a little bit. When i put a new gauge what kind of oil pressure should i be looking to have. The truck is a 89 F30 with at least 205,000 miles. it could have 305k or 405K. Thanks Kevin