I have a 94 XJ6 with 126,000 miles on it. Yesterday, out of the blue, the oil pressure dropprd to zero. I've checked the oil level and it's fine. Replaced the filter, and when I drove it again it seemed fine. Oil pressure was at 4-5 whether driving 55 or at a light. Then, as the car got warmer, it would fluctuate with acceleration. Drive 55, it's at 4-5. Take my foot off the gas-it's at zero. Finally when driven for a little longer, just stayed at zero. Oil light comes on as well. No strange noises at all. Seems to run just fine. But that light and pressure gauge are scaring me. Every time I start it cold, the same thing happens. Drove it 34 miles yesterday and like I said, no strange noises or engine overheating at all. Anyone have any ideas as to what's going on? Oil pressure sending unit, oil pump, false readings, relays etc.? I use 10w-30 btw. Always change it regularly.

 

It is probably the pressure transmitter, but you should really check it out with a pressure meter.

Some shops may have such a device. Essentially you unplug the transmitter, and plug in the pressure meter. This measures the pressure directly without using electronics. A lot of shops have spare transmitters instead of meters, so swap out and see what happens. If pressure is restored on the gauge then the problem is cured, if not, its time for more investigation