Do the newer magnum style thermostats flow enough

OK, dunno on the NAPA brands' quality or not. OK, that makes sense on the old 160 t'stat. BTW, the t'stat opens due to heat so you have to have some heat above the opening temp to get it to stay open. My /6 runs 10-15F above the t'stat temp in warm weather.

Sounds like you are god now. Glad we could help... LOL