Hey guys,

First I don't think it's normal (if you have a proper functioning cooling
system, very well sealed inner head gasket and/or operating crankcase
bleeder) that even at high outside temp the cooling fill tank level move
more than 1 or 2 inch at the most in the filling tank. Andrew is right,
change the expansion cap and double check the expansion tank if it holds
pressure. Another possibility could be that the coolant mixture (50/50)
and/or propriety are not well calibrated. If it happens only at high
outside temp, I am pretty sure that the coolant should be change for some
fresh one. If the coolant as been change, is it of good quality and does it
have the proper mixture.

About idling before shutting down the engine. (I really like this subject)

This is a particularity of Turbo engine, I will try to explain myself in a
proper English (He he he); At high speed, the turbine (Turbo) main shaft
and/or bearing have a tendency to propel most of the oil coming from the
little turbo oil line/nipple away from the shaft. So if the engine is shot
down without idling for a few second (15/30), when you start back the
engine the turbo shaft and bearing are spinning with a limited amount of
oil. With time the Turbo life will be reduce by haft. Just so you know, I
had a Honda CX500 Turbo and CX650 Turbo, Yamaha Seca 650 Turbo and 2x Kawa
GPZ 750 Turbo motorcycle. I blew 3 turbo on the last GPZ engine wile drag
racing.

BUT, this principle somewhat apply to all engine parts on atmospheric
engine (non turbo) also, the basic rule is to get the oil everywhere at the
right place for the next start-up. Never suddenly shut down an engine after
high revving this one, especially for those that don't use their Westy
often, remember the noisy lifter problem!!!!!! (Not exactly the same
principle but still! The lifter decompress after sitting in the driveway
for a wile)
On the opposite, this is another good reason to let the van idle for a few
minute or so at start-up (when cold) even in hot weather so the tick 20W50
oil can slowly and properly make it's way to all critical parts that need
lubrication. (ESPECIALY ON OLD ENGINE=lower oil pressure)
The worse thing you can do with a Westy is to start the van, raising rpm at
the same time and start running the van forward in the first 10/15 seconds.
ESPECIALY when your van is not your daily rider.

I fly (rental) C-152, C-172, Warrior and Arrow 2-4 seater planes. If I
don't let the engine come to operating temp before raising RPM I will be
kick out of this rental place, period. On the contrary, if I let the engine
idle for too long I will be kick out of the rental place also.

Cheers, Ben