My 98 Grand Caravan 3.3L (130K miles) is giving me problems again.
First problem began a couple weeks ago when I noticed a whine that
appeared to be coming from the back of the engine (possibly on the
driver's side, but I'm not certain). It only seems noticable when
idling, coasting, or driving at low speeds (maybe under 25mph). It
sounds like when you blow up a balloon, then pinch the opening and
slowly release the air - that kind of high pitch sound. And when I
accelerate, it seems to go up in pitch and then disappear. About a week
ago, I noticed the Service Engine Soon lamp came on, with no noticable
variation in performance. A couple days later, the car overheated. It
has since had overheating problems. And when I sit at a light, the AC
starts to blow warm air.

In April I had the water pump replaced after it seized up, and new
coolant was put in at that time. I replaced the thermostat, air filter,
and PCV valve last week. The head gasket is less than 2 years old. The
fan relay switch and O2 sensors have also been replaced in the last
year. Serpentine belt seems to be in pretty good shape. I believe it's
maybe a year or two old, tops.

The AC problem, I am assuming is happeneing because the fans aren't
kicking on. Last time that was the case, the fan relay was replaced and
solved the problem. I need to double check that the next time it
overheats.

The crossover pipe has been an issue for quite a long time (maybe 5
years), but I have not been able to find the part as it's apparently
not made or always on back order. I realize this could be part of the
whine problem.

I was thinking a vaccuum leak or the existing crossover leak could be
the causes of the whine. The fans not kicking on could be a problem for
the AC. I have no idea about the overheating, unless maybe it's plugged
up. Radiator hasn't been flushed in at least 5 years. I am guessing the
AC and overheating ARE possibly related, and the whine is possibly
unrelated. But I am certainly no expert. Just wondering if anyone has
any ideas to throw at me.

Was thinking about taking it to a dealer to at least see if they can
give me a diagnosis.

Thanks in advance.