300tdi low oil pressure when engine has warmed up. I am hoping this thread may help others. When my engine had warmed up the oil pressure dropped off to about 20psi at 2000rpm. I changed all normal things i.e. oil filter,water thermostat, radiator, oil pressure relief valve, big end shells, fitted oil cooler thinking oil was breaking down with heat. Finally found problem was crud in the head of the oil thermostat. There is a natural restriction where there is a support bar for the thermostat and the oil has a 90 degree turn to get into the filter. What was happening was when the oil thermostat was activated by the oil temp, it moved, restricting normal flow to the filter. This then forced the oil to flow through the oil cooler, which was then blocked by the crud, reducing the pressure. So if you have good oil pressure until the engine warms up and then drops of rapidly, check your oil themostat. My oil pressure now is 40 psi at idle and 70 psi at 2000 rpm when engine warm.
