I have a 88 lincoln towncar just got new raditor water pump and thurmstat but it is spraying out the back side of the engen can a block seal fix that

You need to find out exactly where its leaking from... a gasket or a freeze plug. Either really need repaired properly if you expect to hang on to the car as both can suddenly give out if not worsen. Any sort of sealer is going to be temporary at best in this situation.

Smoothy is right... but it might have been installed improperly.