I drive an 04 dodge ram quad cab 1500. 4.7 l motor. My temp gauge reads hot when driving on the highway, meaning at 70 mph for about 20 minutes of driving the temp gauge starts reading way past the mid mark, when I get down to lower speeds it gradually starts to come down, depeending on the ambient temp outside. I have replaced the thermostat, flushed the system, bled the air out of the system. How can I tell if my fan clutch is bad? I don't want to start replacing parts at will to have the same problem occur, does anyone out there able to help me diagnose this issue?

Do you have an auxiliary transmission cooler? Since synthetics run cooler, I'd only use synthetic engine oil, transmission fluid, and gear oil. Be sure and only use a 50/50 mixture of antifreeze and distilled water. Mineral buildup can develop quickly from tap and well water and restrict the radiator. You may need to replace the radiator or get it rodded, if passageways have become partially blocked.

This may help you:

https://www.askmehelpdesk.com/cars-t...tml#post235973