Overheat, towing in traffic.

[Chuck Tribolet]

I have a 2001 PF SE with manual transmission. This afternoon I was towing my boat uphill
in heavy stop and go traffic. Air temp was 72-74F. The PF overheated. I caught it before
the temperature gauge hit the first bold black line at the top. I couldn't safely pull off for a minute or so.
My wife wisely flipped on the heater full and we got it stopped, shutdown, and the hood up before it got
to the second bold black line at the top. Trailer was bout 2200 pounds, truck had the two of us and
dive gear (about 500 pounds of people and gear). As it started to suck the overflow back in, I kept adding 50%
antifreeze. It took about three quarts between what it sucked back in and what I added to the rad after
it cooled down.

I had the antifreeze mix with me because Friday I'd noticed it had added a bit to the overflow,
which I pumped back into the rad.

After we got it cooled off and topped up, we fired it up and headed home with clear sailing on
the freeway (the place where it overheated was the very end of the stop and go). The gauge
was normal all the way home. After it cooled down at home, I pulled the vent cap and added
a few ounces more 50%.

Because it was fine on the freeway, I'm guessing the problem is the fan clutch.

What do you folks think?

[Towncivilian]

Fan clutch sounds reasonable. When you spin the fan blade by hand, is there some resistance? IIRC, mine will spin about half to three-quarters of a revolution before stopping by itself, and there is some resistance to beginning the spin as well. I believe if there is little to no resistance encountered and the fan blade spins freely, the fan clutch is most likely bad.

Also ensure there are no bugs, leaves etc on the front of the A/C condenser as this will impede airflow. I would also inspect your radiator cap according to this TSB.

[Chuck Tribolet]

I think the fan should spin fairly but not completely freely when the fan clutch is cold, and progressively less freely as it heats up.
The idea is not to waste power moving lots of air when things are nice and cold, either because it's just fired up, or it's sailing
down the freeway blowing 70MPH air through the rad, or coasting downhill. There will be some resistance, kinda like it's full of
stiff grease. Anyway, my fan clutch behaves this way, at least cold. As the clutch heats up, it will provide more and more resistance,
moving more and more air.

At $150 ea, I've Googled up some test procedures. Watch this space.

[Buzzman]

As it started to suck the overflow back in, I kept adding 50%
antifreeze. It took about three quarts between what it sucked back in and what I added to the rad after
it cooled down.

The fact that you had to add 3 QUARTS should have set off alarm bells.
Where did it all go?
Sounds like you have bigger problems than just a fan clutch.

[Towncivilian]

Indeed, this is why I suggested to inspect the radiator cap - it could have pushed fluid to the overflow reservoir unnecessarily. Was it apparent if any fluid had come out of the overflow reservoir when you lifted the hood after the initial overheat?

[Chuck Tribolet]

The radiator cap is reasonably new and looks fine.

Yes, the overflow tank had itself overflowed.

I forgot to mention that for about the first 30 seconds after I popped the hood, there was a buzzing sound (like a 1960's
electric alarm clock) coming from the area of the throttle body. The engine was off at the time of the buzzing.

[Towncivilian]

The buzzing sound may have been the idle air control valve stepper motor. I'm not sure if you've ever noticed but after shutting the engine off (or setting the ignition from ON to anything lower), you can hear some clicking noises for several seconds. I'm almost positive that specific noise is from the IACV. Try it and see if the sound is familiar.

Did you manage to perform any tests on your fan clutch?

[Chuck Tribolet]

IACV sounds like a good bet.

Testing this evening. Yesterday was consumed with helping my wife get her condo ready to rent.

I Googled up a few tests, and will add one of my own: Warm up thoroughly. Let sit for a bit to get the fan clutch up to temp. Hood up, see if it's a bit stiffer. Put a sheet of newspaper in front of the rad, hood down. Run until the temp gauge moves to 3/4, stop engine, hood up, check stiffness.

I really think this will turn out to be the fan clutch.

[Chuck Tribolet]

Well, even with a sheet of paper blocking the front of the rad and 7-10 minutes of fast idle (2000-2500 RPM), the
needle never moved off its normal dead-center position. And when I shut it down after that, and left the hood
down for five minutes to give the clutch a hot soak, there was no change in stiffness.

One thing I did notice is that the fan blades are swept back about half way out their length. And there's some
cracking in the plastic part of the fan where it attaches to the coupling. And there's about 3/4" of clearance
between the ends of the fan blades and the shroud, which seems a bit much.

[Towncivilian]

Every VQ35 fan I've seen has cracks around there, and many have reported cracks lately. I replaced mine with one that has fewer cracks. Is it such a big deal? I have not read of an instance where the fan breaks apart due to cracks.

I think that clearance is normal. I'll try to remember to look for you.