Thanks to Tom Forhan for inspiring this idea.

All 2.1l wasserboxers have an oil/water heat exchanger neatly sandwiched 
between the oil filter and the block.  It is about 4"x4"by 2" thick, with an 
inlet and outlet pipe, 16mm ID.  It is spliced into the coolant loop to keep 
the oil temps down.  Wasserboxers thus have a built-in waterheater!  The 
price for one of these units rebuilt is $157Cdn and I would bet it could be 
fitted to maybe all vanagons and loafs! Filters all look to have the same 
mounts.

Options are:

1) Heating shower water - bypass the regular coolant loop with a tube splice 
and connect new tubes to a 5gal insulated tank, under the bench or in the 
wardrobe, or even use the existing water tank.  If the tank was high enough 
above the oil cooler then thermo-siphoning should be possible, just bring 
one pipe well up into the tank, for 'hot in' and take the return off low. 
High tech option, install a thermostat in the water tank to control a 
circulation pump. Don't know how big a boost the oilcooler gives in cooling 
the oil, none of the 1.9l engines have them, but you still get (some) 
cooling via the shower water.

2) Aircooleds get wasserboxer heating system - worried about oil temps? 
added an extra cooler to foolishly squander that heat on the great outdoors? 
Recycle it into your bus!  Oil cooler unit, vanagon rear heater unit, some 
tubing, and a small water tank with pressure relief valve should do it.  A 
water temp gauge might be nice for info.  Water tank could be a vanagon main 
coolant reservoir with cap, and get the overflow reservoir too, in case it 
boils over!  I bet about an hour in a junkyard and <$100 would get nearly 
all the parts you need, including the dash switch.  A circulation pump would 
likely be needed.  Tieing in a large storage tank would get you the shower 
option. :)

Some ideas for you to ponder, rub-a-dub-Vdub.  The Australian camper 
conversion company Trakka use a metal tubing coil inside the 50litre hot 
water tank to run hot coolant through and heat their shower stuff, takes 20 
minutes at idle to get hot water 'they say'. This could be spliced into the 
rear heater loop and controlled by its valve. Simple enough to run piping 
over to the water tank in a Westy and put the coil inside via the big 
cleanout lid.

Tim Smith