My son has a 1994 Ford Mustang. He put on some fancy expensive oil filter when he changed his oil. It oil pressure began to vary from normal to very low out of normal. I made him change back to the recommended oil filter and oil and the problem seems to have gone away. He still see an oil pressure drop as the engine warms up and increases as he revs the engine. Is it common for a Ford Mustang oil pressure to change from high normal to lower normal in normal running?
Oil pressure will incease and drop when oil gets thinner, check he used correct oil grade