I had a similar problem on my 351 Cobra after I replaced the electric motor my single blade Flex-a-lite fan. The engine got to operating temp and got hotter as I drove it. I brought it home and found that the plug on the electric motor was reversed. I took a sheet of paper and put it in front of my grill and the paper blew off. I reversed the wires and the paper stuck to the grill. My next drive the temp never went above 180. I also switched my coolant to the waterless Evans and have been pleased. Hope your problem is as simple as mine was, just check and see if your fans are ''pulling air'' through the radiator and not pushing.