I think id go for the thermostat first, you can check these with a bowl of hot water but I just replace them 1st thing cause theyre cheap.
Water pump, on an old truck I had, the circulator was made of plastic. It had a crack in it, but not all the way through. Worked fine until about 30-45 minutes into it then it would expand and not circulate water. On a cooler day it would work on and off. Drove me crazy...
On an old f*rd of mine same prob, just under the red, I replaced everything I could think of to get it to cool down, Finally bought a fan shroud at a junk yard and that solved it, it was sucking air from all over and not actually pulling any through the radiator. And it was proper distance to the radiator.
I would keep an eye on the gauge while driving. Now on the freeway does it still do this? Or just parked? If you have to much antifreeze in it itll over heat also.
Good luck, Jeff
