First off....I don't know much about the cooling system, so some of my questions may be very elementary....

Taking VX on a trial run tomorrow to test for overheating. Going to be 103 air temp in Phoenix, and A/C will be running coldest setting and fan at highest speed.
It's about 200 miles round trip. About 3 hrs of it will be city driving around town doing errands.


  • Today noticed I could hear kind of a whining/humming from the engine when A/C was on, and I had driver window down.
    It stopped when I turned A/C off.
    Heard it mostly when slowing for a light. It slowed as truck slowed.
    but never stopped completely...I assume this is the fan?
    I also hear a clicking sound and then a hum when I turn A/C ON... I assume that's the A/C compressor kicking on/off?


  • Does the A/C control the fan clutch when it needs it? Since the fan obviously runs w/o A/C, I'm wondering if the A/C can cause it to speed up when it recognizes the need. Or is the fan just responding to the engine temp it's reading, regardless if it's the A/C causing the strain or any other factor?


  • If the A/C fan speed is lower, is that a lower load on the fan clutch?


  • I believe I should keep the A/C temp at the coldest setting, to keep the compressor working at as max as I can get it, correct?


  • If I drive in D3 to keep the revs higher, trying to tax the engine even more, will that dramatically skew my test? Or can I go in D3 for a while, then go back to normal D4?


  • I don't really want to turn off the engine to allow any cooling whatsoever, but, based on my Las Vegas trip last month, it really didn't cool off much, even after an hour. Is it negligible?


  • There's a short stretch of Interstate 17 that raises over 2000 ft in elevation in just a few miles. Common area for cars and rigs to overheat. Will I tax the engine a bit more if I go up this steep section slower, which means less air flow into radiator?
    The right lane is often moving at only about 30 mph because of many big rigs.
    This steep stretch is on the return trip, so maybe it will reveal something.


  • Any other TIPS OR SUGGESTIONS/DO's/DON'Ts to test for overheating?


p.s....Hubby is on stand by to come get me while roadside assistance is on the way, if necessary.