Here's my oil system priming procedure for 3800's (this assuming you have the timing cover, oil filter adapter, oil pickup, and oil pan installed)...
1) Fill engine with about 4 qts of oil.
2) Using a cut plastic wire tie and new/empty oil filter, shove the wire tie into one of the smaller holes that surround the center hole so it holds open the anti-drainback flap inside the filter. This is a very important step and if you don't do this, you won't be able to prime the engine.
3) Fill the filter with oil and screw it onto the oil filter adapter (make sure the cut-off plastic wire tie stays in place and doesn't come out or get shoved all the way into the filter).
4) Connect a 1/4" NPT thread to 3/8" or larger nipple adapter fitting to the oil pressure sending unit port on the oil filter adapter housing and then connect a 3/8" ID or larger clear nylon hose that is about 2' long to this nipple. Install a funnel into the end of the hose and hold/secure it upwards from the oil filter adapter housing.
5) Fill the tube with new/clean engine oil (can fill the funnel some).
6) Using a socket wrench, rotate the crankshaft COUNTER-CLOCKWISE slowly. When you do this, you should notice the oil level in the clear nylon tube start to drop. Keep adding oil to the nylon tube and keep rotating the crankshaft until you've added about 1/2 pint of oil to the engine this way.
7) Remove the nylon tube, funnel, and 1/4" NPT nipple. Reinstall the oil pressure sending unit or a mechanical pressure gauge.
8) Using a starter and battery, crank the engine over (with no spark plugs installed in the heads if the heads are installed on the engine) until you get a good oil pressure reading on the gauge or from the sender. The stock sender will measure about 0 ohms of resistance at 0psi and will rise in resistance as oil pressure builds (so you can test pressure using a stock sending unit and ohm meter).
9) Once good cranking oil pressure is established, unscrew the oil filter, remove the plastic wire tie piece from it, and then reinstall. If you cannot get the wire tie piece out of the filter, discard the filter and get a new one - prefill with oil before installing on the engine.
10) Verify proper oil level in the engine prior to starting and then re-verify after it has run for about 30 seconds or so.
NOTE: If you can't get any oil pressure after cranking the engine over for 15 seconds or so (running disabled), STOP and repeat this procedure. If you don't get oil pressure upon starting and running the engine for more than 5 seconds, SHUT IT OFF and repeat this procedure.
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[This message has been edited by Darth Fiero (edited 07-26-2013).]