Originally Posted by Frango100
Welcome to the garage. No experience on the 4.0 myself, but i understood that the crank bearings can wear and lower the oil pressure.
If the pressure really becomes 0 at idle, you should get some mechanical noises. The hydraulic valve lash adjusters will start making ticking noises.
You could put a new oil sending unit on it first, then you know for sure if the pressure is low.
Agreed. The oil pressure sensors on the 4.0 were notoriously bad--but quite cheap and simple to replace. Or, your mech should have a precision one that can be used to check yours.
I'd expect a bit of cold clunking if the crank bearings were worn enough to drop pressure notably.
Just in case, you might want to drop a can or two of STP Oil treatment into the engine, as it can help avoid casual damage--some folks ran the Baja with an oil leak and just STP.