I picked up my tractor today after the motor overhauled. The tractor is a 1961 MF 35 with the perkins diesel. The motor was pulled and completely rebuilt with all new bearings, pistons, ect. The tractor idled for about 15 minutes then I hooked up a bush hog and began to do some mowing. After 30 min or so I noticed the oil pressure gauge was reading right on the red and green line on the low end of the gauge. I stopped working and headed back to the barn and shut it down. I talked to the mechanic and he said the gauge could be back or it could be because of the break in oil. He told me he hooked a digital gauge up to it when he was running it and the oil pressure was good. Any ideas what could be causing this? Thanks!