[Rich Biebel]

Wix does make Napa filters and the numbers are the same but with an added prefix number for Wix denoting what type filter it is...

For example

Wix.....51061
Napa...1061


Add a 5 for oil
Add a 4 for air
Add a 3 for fuel...


We use Wix pretty much exclusively at our place of business and I use Wix 51061 R on my own race engine

Having low oil pressure on a warm engine usually indicates very loose clearances or an internal leak.