I live in the southwest where it's "hot". Average temps above 110.
My '77 450SL with 95k miles is overheating during my commute from Yuma to Lake Havsu City AZ approx 150miles. I have taken it to several shops in the area non of which are MB dealers. I have had the radiator and thermostat replaced, checked for proper cataletic converter flow and still have this problem. What can I check next?

Thakx
MY450