Can I use UV dye to find an oil leak, after having drained the oil?

Question

We drained the oil to change the oil pan. Confirmed a tiny bit of light is visible through it after removing it, so it was a source of a leak.

I then noticed what looks like it could be another (smaller) oil leak further up. With the oil already drained out, what do I do next?

Do I need to add the recommended 5 quarts and UV dye? If I do that and find another leak, those 5 quarts will be drained out again and wasted. Unless it's safe to re-pour it from the drain container back into the original containers than eventually back into the engine... But I'm weary of doing this because so much rust is flaking off underneath, that I think what would wind up in the next cycle in the drain container would be contaminated with things that would wreck the engine.

Is just adding UV dye going to help at all? I know I obviously can't turn the engine on with the motor off. Are many oil leaks only going to happen when full of oil and turning the engine on?

I know in the grand scheme of repairs, wasting 5 quarts is nothing, but trying to figure out if I can avoid that.

Lesson learned, should have been more observant to have realized I needed to use UV dye first.

Answer 1

The only way to use UV dye to find leaks is to add it to the oil and run the engine, you can't splash it around a few places and hope it runs out somewhere you can see, it has to be circulated with the oil under normal operating pressure.

I appreciate that you don't want to waste oil, and you could probably filter out any rust or dirt using a coffee filter before reusing your oil due to your valid concerns about contamination. I would suggest though that you don't need to do any of that as it's a small leak. Engines develop small leaks over time and not all of them are worth the time and effort to fix, depending on the source. You could clean the engine and run it normally, then use the oil trail on the clean metal to find the source without a dye. Once you know the source you can make a determination of whether it's worth fixing or not.