Who makes a good water circulating pump for a bbc 502 MPI.

I've used sierra's and merc's, the only difference was price.

I would my the Merc water pump it has a better warranty.

I would use merc or mesco
mesco has same warranty but cheaper plus its painted black just like the OE. I use them at work all the time (mesco) unless its a merc warranty issue. If you are in toms river call baywood marina in brick 732-477-3322 ask for billy in parts.
tell him joe sent you. Joe
ps they have a boat us discount also