Last week a changed the oil in my 1997 4.0 sport. Since I work at a ford dealership I used a motorcraft filter and 5w30 synthetic blend. Now today i was driving at about 45mph and noticed the oil pressure guage slowly started dropping to around 20psi. When I came to a stop the oil pressure slowly dropped some more to around 15psi or so then comes up to twenty then back down. I went to check the oil and when i pulled the stick out it was dry, checked again two seconds later and im reading full??? I dont think I have an oil pump problem but im just a little worried. Anyone had this problem before? What conventional oil are you guys running in the summer?