New owners often find themselves mystified by the cooling system of the Vanagon. Which is understandable, considering that it’s kind of an oddball setup.
A little historical context and a quick tour should help ‘splain things.
Most water-cooled cars, including the one you probably use as a grocery-getter, has the engine up front, right behind the radiator. So, the entire drivetrain is in one compact package.
A water-cooled engine relies on a radiator to dissipate heat, and the best location for a radiator is out front in the stream of fresh, cool air. To connect this rear-mounted engine to this front-mounted radiator there is a pair of long steel or plastic pipes running the length of the Vanagon’s underside.
In this regard the Vanagon/Transporter is indeed an odd duck, but at least it’s in good company; other notable production vehicles to utilize this unusual arrangement are post-1998 Porsches and the DeLorean DMC-12.
This design also calls for a separate coolant expansion tank and a coolant reservoir located near the engine in the rear, and here is where much of the confusion commences …
Let’s take a quick lap through the Vanagon cooling system.
When you fire up that little waterboxer or diesel and hit the road, excess heat from the cylinder heads is immediately transferred to the liquid coolant, which the water pump circulates back through the cylinder jackets & heads again, in a short closed loop. This prevents over-cooling and helps the engine quickly warm up to proper operating temperature.
Once the coolant reaches about 190˚F (87˚C), the thermostat opens and begins routing coolant via the long coolant pipe way up to the radiator. Here, fresh air draws away the excess heat, and the now-relatively-cool coolant goes back to the water pump and engine via the return pipe, completing its circuit.
Like any liquid, engine coolant expands as it is heated. As the name implies, the Expansion Tank manages this expansion; a pressure-sensitive valve built into the tank cap allows excess coolant to vent via a small hose to the Refill Tank. In a well-functioning closed system, the Expansion Tank will always be completely full of coolant, with no air space.
The Expansion Tank also has a built-in coolant level sensor, which detects a low fluid level and triggers a flashing red warning light in the dashboard temperature gauge. This same warning light may also be triggered by separate coolant temperature sensors, located elsewhere.
This excess coolant flows to the Refill Tank, located just inside the license-plate access door, and which serves as a coolant reservoir. When the engine is turned off and begins to cool, the coolant in the system now contracts, and an equal amount is drawn back into the Expansion Tank from the Refill Tank. The Refill Tank’s volume will rise and fall with coolant temperature, between the MAX and MIN marks.
NOTE: These tanks are often and variously referred to by owners and even by the vaunted Bentley Workshop Manual as the reservoir, pressure, overflow, or burp tanks, sometimes interchangeably, which certainly doesn’t help matters. Expansion and Refill tanks are the terms most consistently used in both the Owners Manuals and the Bentley.
In addition to these basic system components, there is also a heat exchanger located inside the dashboard, with standard controls on the front dash panel, as well as a secondary heating element beneath the rear bench seat.
When the dash temperature control is set to “Warm,” a valve is opened, directing hot coolant from the engine to the heat exchangers to provide warm air for the cabin. This coolant is then routed back to the Expansion Tank for re-distribution.
In a later article I’ll cover how to properly bleed the cooling system of all air bubbles after a coolant change or other work. But, it may be helpful here to understand the interaction of the Expansion and Refill Tanks in daily operation.
Though in theory a closed loop, the Vanagon’s cooling system can sometimes develop bubbles or pockets of air, caused by incomplete bleeding following a coolant replacement, a leaking hose or clamp, or by a failing cylinder head gasket allowing exhaust gases into the cooling system.
These air bubbles will tend to (but not always) make their way to the coolant Expansion Tank, where normal operating heat and pressure will usually expel them to the Refill Tank.
As any child with poor table manners knows, a drinking straw in a glass of chocolate milk allows bubbles to be blown into the glass, but only liquid can be drawn back up. This is exactly how the Vanagon Refill Tank functions; it accepts both coolant and errant air bubbles from the Expansion Tank when hot, but sends back only liquid coolant as the system cools. In this regard, the Refill Tank functions as a sort of one-way valve, serving to ‘self-bleed’ air bubbles out of the system to a great degree.
I hope this clears up some of the common questions about the Vanagon cooling system!