[v8volvo]

Is this on a newly rebuilt engine that has never been run yet? (I.e. the oil system is dry and you are trying to prime it for the first time before starting it?)

It is definitely a challenge to prime the oil system for the first time on these engines especially if the oil pump has even a slight amount of wear on the pump lobes or on the pressure relief piston and bore. But I have had these steps give good results:

1) Disassemble oil pump, coat all internal oil pump surfaces AND the pressure relief piston thoroughly with engine assembly lube (needs to be done with front end of engine still apart of course, you might not want to take it all back apart at this point) -- this helps the pump create stronger suction to pull oil up from the pan

2) Use a very lightweight engine oil for the first start that can move easily up the pickup tube, cheap conventional gas-engine 5W20 or 5W30 works well (you will drain it out after running a few minutes anyway), and overfill the crankcase by 2 or 3 quarts -- this won't hurt anything for low rpm running and reduces the distance the pump needs to pull oil up from

3) Remove the injectors -- this allows the starter to spin the engine (and oil pump) as fast as possible

4) Fill the oil filter up with oil before installing it

By doing these steps my experience has been that the engine will build oil pressure in less than a minute of cranking on the starter. After you see oil pressure come up, best to continue cranking it on the starter a little while longer to ensure oil reaches not just the pressure sender location but also the cam bearings, turbocharger, etc. You can then reinstall the injectors (with new heat shields) and start the engine.

The other option is to buy or borrow a pre-oiler apparatus that uses shop compressed air and screws into the location of the oil pressure switch on the side of the block, then directly primes the oil galleries that way. But that requires expensive machinery and access to shop air, and it runs a risk of contamination since it involves feeding oil into the lubrication passages without going through the oil filter.