I use a can of engine paint, then I let it sit for a few days... After this is done I use a red scotch brite pad and scuff the enitire block, then seal and paint...
I do this for the reason that the engine paint will bit to the bare block ( it is made for that purpose ) it is also heat resistance for up to so many degrees and the car paint bits to the engine paint. I have done this many times and even sprayed kandies on it and to this day it has worked...
I also do the same steps on motorcycle engines, but I spray a little dryer because the engines are air cooled instead of water cooled...
Hope this works for you.......

:cheesy: