I recently acquired a 550 diesel and the gauges didn't work and when I got a new oil pressure gauge it reads 15 psi cold and around 2-4 psi hot at 1500 rpm. the motor runs good and has plenty of power but it does smoke a bit cold but that clears up at working range. A buddy told me to check the oil pressure relief valve as he said the spring might be weak or broke so when I took out the plug below the oil filter I found the spring and plunger are not there at all ! This worries me as I don't know much about tractors and this is my first one and from the research I've done this could be my oil pressure problem. Any info from anyone about this would be very help full and if anybody knows where I could get the replacement parts that would be great to.