stock a/c compressor as air compressor

i converted my stock a/c compressor to pump air to my 12 gallon tank.. works GREAT!! goes from 0 psi to 160 in less than a min @ 2500 rpm.. what kind of oil should i use in it?? how often should i fill it?? how do i know when its full and will it hurt to over fill it?? a friend of mine has a similar setup and his advise on filling it was " add some oil when the compressor sounds like its getting loud!!" not bad advise considering  that his has lasted a long time so far, just wanted to see if there are any other ideas out there.. ive been using a/c oil so far and that sh!t is $10 for a lil bottle!! hoping to get a cheaper, yet safe idea for oiling... thanks all for any advice......

30 weight non-detergent

Since you have an 02 with the 4.7 id think you have the same ac comp as me....Mine worked wonders for a couple weeks...I used 30 w non-detergent like Waylayed said...Pumped hella fast. First time I had to actually push it a lil bit...it burned up. Id watch it....I suggest upgrading to a york 210...that's what I did...beeen running it daily since January without a single prob. I got it at a junk yard for $25...I can make you a bracket if you need it...i have pics in my profile of it installed.

hey could something be done with the ac comp on a 96 ranger i'm not tryin to steal the thread just curious on how you all are doin this

thacrue78- if you make a bracket that fits on dakotas hit me up with the price.

thanks fellas... outcast, if your compressor has an oil fill nut on it then i believe it will work.. what i did was unhook the a/c lines, tapped the inlet and outlet holes to accept threaded fittings, put one of those lil import oil vent filters on the inlet side and ran 15ft of hydraulic line (airline will melt from the heat) on the outlet side to the tank with an oil/water seperater and check valve at the tank.. wire the compressor to a toggle switch if you got gauges or pressure switch if you dont have gauges. took about an hour and $50 for used parts.. i left a viair 480 hooked up to the tank just in case the a/c comp fails.. good luck dude...   oh, what cars or trucks are the york 210s found on???