What's too hot?

I had problems with mine when I had an electric fan on mine.
It was a 14 in.fan. I got , I think a truck rad. in mine. About
2 to 2 1/2 thick. I went back to the stock clutch fan and its
OK. I run a 160 degree stat. Gets up to about 160-170. Just
my input. Good luck, Brian.