L Series Diesel oil pressure warning light.

W reg Freelander with the L Series diesel engine. The red oil pressure warning light stays on when the engine is first started, the light will go off if you blip the throttle and stays off until the engine is switched off. If restarted immediately the light will normally go straight out again, but if left to stand for a while the fault will return. I have changed the oil pressure switch. I have removed the sump to check the oil pick up pipe which was fine. I have removed the oil cooler / heat exchanger pipes and I can blow straight through so that is also clear. I have removed the pressure relief valve spring and plunger which both appear to be ok. I have changed the engine oil and filter but the fault is still the same. My next step would be to remove the oil pump, however I have seen these symptoms described on several forums with no solution posted. A new oil pump seems to be difficult to find on line and I can't find anyone who supplies a oil pump repair kit.

Your help would be appreciated.

Put a proper pressure gauge on it so you know exactly what the pump is giving.

I took the oil pump off and the housing was cracked. A new oil pump and gasket was £200, cheapest place I could find was Famous Four. Problem now fixed.