FYI for those people with overheating issues with their VX

[tom4bren]

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?
  
  Bingo. Hopefully the humming is coming from the new clutch & will go away as it breaks in. Do take the time though to check to see if anything is rubbing. Double chech the shroud for any signs of contact with the fan blades (they change shape slightly as the fan is spinning & may contact while in motion but not at static).
  
  
• 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?
  
  The fan should run all the time while the AC is on. The engine turns it on & off as needed with temperature. The fan is not adjusted for speed by the AC (it's either on or off). The fan speed will change with the engine speed though. In reality, the fan speed isn't being adjusted to run faster with the engine speed to pull more air - it's simply a matter of the fan being driven by the engine and spins at the respective speed.
  
  
• If the A/C fan speed is lower, is that a lower load on the fan clutch?
  
  No. AC is on or off just like in your house. It turns on to get the cabin temp down to a few degrees below what you set it for & then turns off. When the cabin temp rises a few degrees above the set temperature, the AC turns back on & the cycle starts all over. The cabin fan just circulates the air.
  
  
• 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?
  
  Yes but only around town. It sounds like your overheating issues are associated with the slow crawl rather than highway speeds.
  
  
• 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?
  
  With the engine running at higher RPMs, you would certainly be putting more stress on the cooling system. Just don't over rev your engine for long periods of time (remember that you've already experienced oil consumption at highway speeds that you don't on 'round town driving). Hate to see you blow your engine trying to test your cooling system.
  
  
• 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?
  
  Turning off the engine is certainly the best bet if you're starting to run hot so that the engine will stop trying to dump more heat into the already hot system. It is however a 300 lb block of metal sitting inside a fairly closed chamber. It'll take a while for that heat to dissipate. Open the hood & it'll cool much faster.
  
  
• 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.
  
  I don't think you'll see much difference between going 30 mph & going 60 mph up that hill. When your cooling system is operating correctly, I'm guessing that the fan almost never turns on above 20 mph. The radiator fan on my Eclipse doesn't come on automatically anymore (I know ... I know ... I should fix that - I will when I get tired of procrastinating). As long as I'm moving at speeds above 15-20 mph, I don't have to worry about it. Unfortunately with my commute there is a lot of sitting in traffic so I just hit the AC or Defrost till the temp comes back down (fans still come on when compressor is on).
  
  
• Any other TIPS OR SUGGESTIONS/DO's/DON'Ts to test for overheating?
  

Pray

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

See if your mechanic has a scanguage or a temp guage that you can borrow for your test. If I wasn't using my scanguage this weekend, I'd send it to you. Sorry!

EDIT: Of course everything I've said is completely inaccurate if it's your thermostat that's causing the problem.