Coolant Flow 2.1l
From VanagonWiki
The 2.1l wasserboxer is a plumbing masterpiece. Given that neither the venerable bug/bus upright nor the "type IV" air-cooled engines to which the wasserboxer owes its heritage were designed with water cooling in mind, I suppose they didn't do too bad a job. It is, at least, a great improvement over their first attempt, with the 1.9l.
Water circulates from the water pump and into the water jackets, directly into the left, and via the pipe under the pulley into the right. From the jackets it flows into the heads. The right head feeds directly into the coolant manifold and the left head feeds into the thermostat housing. From there it gets interesting. When the engine is cold and thermostat is closed, the radiator circuit is blocked. Water from the manifold on the right flows right-to-left through the crossover hose into the thermostat housing, where it joins the water exiting the left head and returns to the water pump via the return pipe along the left side.
When the thermostat opens, the water exiting the right head flows into coolant manifold, into the radiator circuit, and back through the open thermostat. As it's a dual-action thermostat, it not only opens the radiator return pipe, but also blocks off the lower part of the thermostat housing from the left side coolant return pipe. With the return to the water pump now blocked, the water exiting the left head has nowhere to go but left-to-right through the crossover, into the coolant manifold, to join with the water from the right head on its way to the radiator. Reversing water flow. Ingenious.
A picture is worth a thousand words:
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JBange 22:27, 13 June 2006 (PDT)
