The theory is that coolant was flowing through the radiator too fast to adequately cool.
That theory is completely at odds with accepted thermodynamics.
Generally, overheating at highway speeds is water flow related.
But you don't claim to be over heating, just running "hotter",.
You you have numbers?
Highway speeds generate more heat in the engine, so what might be "ok" at idle and no load fails at a higher load. Your recored radiator means nothing on the surface, was it flow tested? What core was put in? Airflow out of the engine compartment can be an issue as well. Air can't go thru the radiator if it can't get out of the engine compartment.
You bring up some very good points.
What bothers me is it acts "funky". A few weeks ago when it was in the high 80's drove it about 20 miles. A little back road driving and then 12 miles of highway driving and it was a nice steady 195. Got off the highway and turned around and right away it started climbing to 215. Drove it 7 miles at 60 mph and when got off the exit was stuck at a light for a bit. Climbed to almost 220. 4 mile back road trip to the house it dropped well into the 190's. This was with the Stant Thermostat.
Yesterday it was cool - in the lower to mid 70's. With the new Milodon thermostat same exact route and it acted very similar. Never exceeded 203 on the highway, and driving back home on the back roads it went down to 190. Idling extended period of time in the driveway was 195.
I don't know the answers off hand on the radiator. I do have that written down somewhere and did a bunch of research before I settled on this core. I might call Glen-Ray for another radiator if I feel the radiator is suspect.
I agree on getting the heat/air out of the engine compartment. Dealing with that exact issue with my cousin's 67 Firebird with a blower.
I am wondering if the aftermarket condenser and tranny cooler is chocking the air to the radiator at highway speeds...........
