Y is my at oli temp light on - 1994 Nissan Pathfinder

If the light is on all the time (not just at idle), DON'T continue to drive it - you will trash the engine. Having oil in the crankcase is not enough, the oil needs to be pumped to all the bearings, etc in the engine. It's possible it's a bad oil pressure switch, but don't take a chance. Have it checked out.

Your head gasket has a leak & it will need to be repaired at a mechanics with costs starting at around £700.00 Or $1200.00

I would want to check the oil pressure with a mechanical gauge or replace the switch next to verify the issue. It could be something electrical or the engine really could have low oil pressure.

potentially you are using to fine a grade oil and the oil is seeping past rings and burning off on startup

sounds like you need a new engine ,if its run with no oil even for a few seconds its will damage the crankshaft

You have a chip on your key,Your ignition has wire that goes bad,You have to get a new ignition and key that has a new chip.

oil pump replacement is common at about 120/150k,

The oil is white because water from the cooling is mixed with it. Stop using the car immediately and fix it (most likely a blown head gasket) or you will destroy your engine in a hurry.

power steering is operated by electric pump on this vehicle, check fuses, check for fault codes if fuses ok

if fuses are all good check oli sending unit it has a cut off built in in case oil presure drops so it can be the problem,,, oli sending unit may be leaking or not if it is bad