I can cross 42" of standing water in my Jeep CJ7 without stalling, but I
can get a stall in 6" of water if I go too fast.

From my off road experience, it is a condensation issue that causes the
stalling in most vehicles.

The cold water splashes onto the hot distributor cap which causes masses
of condensation to form inside the cap.

When this does happen, we just open the distributor cap and spray the
insides with WD40 and away we go again.  Lots of times, we put the WD40
in first which seems to do the trick.

WD40 is a great water displacement fluid.

The other way a car stalls, which can be an engine killer, is it sucks
up water into the air intake.

Most cars have a fresh air scoop for the engine that opens just above
the bumper under the headlight.  So if you get water over the bumper,
Bang!, one seized up engine with likely terminal internal damage.

We watch that on Jeeps.  Some YJ's had a stupid scoop under the
headlight too as one friend found out the hard way.  He was lucky, he
didn't blow the engine because he had the RPM low:
http://www.imagestation.com/album/?id=4292076845

I was on the other side already.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Fill in the blank with either "ignition system" (which could mean plugs,
but more likely would mean coil or related hardware, which is probably
sitting lower than the plugs) or "carburetor". (Can we say "instant
hydrolock, snapped rods, holed pistons, and/or broken crankshaft as the
engine gulps incompressible water"? Sure... I knew we could!).

Of course, for a really hot engine, the answer could be "block"... As in
cracked/broken/shattered/exploded due to the thermal shock.

Alex, I'll take "It varies by vehicle make and model" for 400, please.