Oil in radiator

Hello, i have a rebuilt 383 that has not fired yet. Have turned it over but thats it. anyway i noticed a little oil in my radiator when i was checking the level. What would cause this? I have no water in the oil. so it couldn't be a cracked block or head gasket correct?

1) Pressure test...

2) Are you certain it's engine oil???

Think I'd verify it's not trans fluid if an auto car...


Rad been checked-out???

Thanks, i have not done a pressure test. I am certain its engine oil as its a manual transmission car. Radiator has not been checked out but is a new champion alum. radiator.

how much oil do you see in the rad? Did you rinse out the new rad before using it? Always rinse them out, I learned the hard way at the shop on customers cars. We have no idea what is in a new radiator when they arrive.

that'd be my first start, pump it up to 15 & see if it holds

ok thanks, i'll pick up one of those kits tomorrow or friday, fill it back up and test it. How long should it hold 15? indefinitely?

ideally forever but it will vary & most seep a little. I bought an alum stat housing and drilled it with a .339 "R" drill bit then tapped for 1/8 NPT then screwed in a 1/8 NPT/schrader brass tank valve that sells at O'reillys for less than $3 then pump it up with your air chuck. took minutes from start to finish. Far cheaper than a Stant radiator pump up universal kit tho the kit has the adapter to check the cap also. Holler how it goes. EDIT Drill a miniscule hole in the stat flat ~1/32 or just use your smallest bit (wont affect cooling at all & vastly eases initial fillup time. MORE EDIT monitor your time as you'll hit 15 in seconds! EVEN MORE EDIT stat housing was pot metal or cast iron, just felt like alum when I was working with it