Questions after overheat

[dmessent]

I had a stupid overheat yesterday. I downshifted and the right side of my instrument cluster lit up; figured it was something electrical but in fact my alternator/fan belt had jumped off. A few minutes later I realized the temp gauge was pinned and parked the car. Coolant was audibly boiling, and it was easy to see what had happened to the belt.

I came back later, replaced the belt, topped off coolant (had lost a quart or more), and the car started fine. Didn't overheat when idling for several minutes, on the drive home (3 miles), or again when idling in my driveway. Drove another 20 minutes to work and temp gauge behaved normally.

So I think everything is ok, but I have questions:

1. How the heck did my belt come off? Alternator tensioner was still locked down in the place it was previously. Belt (Continental Brand) was flipped inside out and had some weird wear on one of the shoulders but that could have just as easily happened after the fact. Belt was installed 1k miles ago or less, and I did a visual inspection as part of trying to track down a whine less than 100 miles ago.
2. Haven't checked for oil-coolant contamination yet. Is this just a matter of inspecting the oil dipstick and dipping your finger in the coolant reservoir?
3. Is there anything else I should be doing other than keeping a sharp eye on the temp gauge? Do I need to bleed the cooling system right away or can it wait until the timing belt I was planning on doing in the next few hundred miles?
4. I see where the coolant overflow tube is, but there was also coolant all over my reservoir (late car). Does that mean something on the reservoir failed and should be replaced? Is there another escape point in the system that would not result in a leak after the fact? My driveway was dry this morning.

[jlevie]

Worn water pump bearings can cause the the pulley to cock and the belt to come off.

Excess pressure should have vented via the overflow tube. But cracking of the original expansion tank has been known to happen.