Quote Originally Posted by Hondarally View Post
Highway driving should put a very low load on the cooling system. You're only drawing about 20kw at100, and have bulk air flow. To be overheating under those conditions means either
A) radiator blocked (classic symptom tho unlikely if rad is new)
B) airflow bypassing the rad as mentioned before
Block off excess openings
C) water pump farked. Not drawing enough coolant through the system for proper heat exchange
D) inside of engine caked with scale forming an insulating layer.
Hondarally is spot on, this would need to be checked.
I wonder what is the rating on the new radiator? Being a thicker radiator it will not be as efficient as traditional (large area) radiators and will produce larger air pressure differential (takes more force for air to go through) across the radiator.