20W/50 is shown as an acceptable type, I was just floating the idea it could be the viscosity that might be a contributory factor, but if it's the oil pump that was wearing out, so much the better. Many years ago I had a Ford Mondeo and one cold frosty morning in England it would not start, The engine turned over fine but wouldn't fire up. The breakdown assistance guy told me the oil was too thick, and in the cold weather it couldn't flow into the valve lifters to open the valves. He managed to start it eventually and I took it straight to a Ford dealer to get the correct oil put in. After that, I never had any problems.