I have replaced the oil pressure sending unit on my 1990 FJ 62 Land Cruiser… Interior gauge still sits at bottom… tested gauge by grounding sender wire and observed gauge needle go from completely low to high… gauge appears to be working. Vehichle runs fine and has for ever, smooth engine sounds good mileage. Any ideas… this has be ongoing … yes there is oil in engine…
You could have a weak oil pump, or the bearings are so worn that the pump just cannot build up the pressure. I would ahve the oil pump checked out as well.