I've just installed an after market temp guage and am wondering at what maximum safe tempature is?

I have a 460 in a '68 F-250 with a 4 row radiator.

 

I would not want to see it go much beyond the 200F mark.

 

I guess 200 would be great, but I believe many vehicles have 195 thermostats. The pressure radiator cap is there to raise the boiling point, as does the proper concentration of antifreeze. Maybe somebody with more knowledge than I can answer this, but I think you're OK up to at least 240. That's also where the gauge turns red on my '70 Firebird.

MrBSS