A little background, I just did the timing chain replacement on my 2003 4.0 190k mile explorer. Have about 20k on the new timing chains. Driving at 60mph my "check guage" light went on and oil pressure guage bounced around a little then went to 0. I pulled off the freeway and when I put it into reverse Guage showed pressure. I noticed the belt tensioner was bouncing slightly and sounded like it was making some noise. I got back on the freeway and drove it for another 20 miles then guage showed no pressure again. I kept driving (thinking it was a faulty sensor) and started to hear some engine noise so pulled off again. Got it towed home and just started it again and now it shows oil pressure on the guage. Thinking I need to: Check/replace tensioner Replace sending unit Check oil pressure with a mechanical guage somehow. Replace oil filter My question is if there was no oil pressure shouldn't I have got a low oil pressure light. And if there was no oil, would it have ran for 20 miles? How do you check the pressure with a mechanical gauge? Any thoughts and ideas would be helpful. Have a lot of work in this truck already. Pulling the engine again is not going to be an option.