Cleaning yellow rad fan blades?

Try Clean and Perfect by Natural Chemistry. Very safe on plastics, works surprisingly well if you let it sit a while, then use a mr clean magic eraser sponge, lightly, to agitate and you should be all cleaned up.

 

There was a recent post on this very subject.
I use Simple Green and a plastic-bristle brush (like a toothbrush)
Take care not to use anything that will scratch the plastic.
Rinse with water and wipe dry.
Made mine look like new, even an old beat up one I got off eBay.