My '74 BMW 2002 likes to run hot. I have installed a 75°C thermostat, my radiator is relatively new (less than 10,000 miles), I have a five-bladed fan, a good radiator cap, the hoses are in good condition, and I use 100% antifreeze.
In the city the temperature needle sits about halfway. On the highway, the needle starts to climb to just under the red. Could the water pump be at fault?
Author: Jack Cohen
First of all, 100% antifreeze is a waste of time and money. Antifreeze is most efficient when run per manufacturer's suggested dosages. I would suggest that you add a mechanical, not electrical, temperature gauge. This will permit you to know if in fact the car is operating at 75°C. Electrical gauges are known for their inaccuracy.
After running straight antifreeze, there is a good chance that the waterpump is faulty and that the impeller boss is partially eroded.