my 94 rams oil pressure gauge drops to 0 and oil light comes on. definetly oil in truck. this only happens after 5-10 min of driving. it even started knocking today after 10 min. oil pressure 40 when first started. how do i determine if its the pump or the bearings. when it first starts to drop it fluctuates from 40 to 0 for a while then nothing but 0 and knocking. any help greatly appreciated!

 

Chances are it's a crankshaft and bearings
What engine!!!!!!!!!!!
The FIRST thing I check......
Thrust bearing end play.
from under the front of the truck use a large prybar behind the waterpump pully to GENTLY push the crank pully IN (Don't bend the waterpump pully) then with a smaller prybar pry the crank pully out. you should NOT be able to see it move (if you want to get more precice do this with a dial indicator hooked up)
If you see it move or hear a clunk ..... you need a crankshaft and bearings FOR SURE!!!
other than that your stuck pulling the pan and inspecting the bearings
I hope this helps
John

 

its a 318 motor. if its the relief valve what symptoms would it show?? vs the bearing

 

Relief Valve failure is very rare.... and even harder to diagnose (unless your lucky and it happens when you have a guage on it)
Bearing failure is common and a crankshaft runout test or Visual inspection usually finds the problem