Replaced the water pump last night because we had been losing coolant pretty badly. As I was checking the gauge this morning on the way to work I noticed that the oil pressure gauge was sitting on 0. There had been no indication of low oil and I wouldn't have noticed if I hadn't been watching for the coolant temp. The engine was smooth too. I got out and checked the oil, it was dark so I had to rely on the dip stick. There was pretty dark oil on the dip stick just a little past the middle of the hash marks. Checked it again cool and there is oil just past the full mark.