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OVERFLOW BOTTLE
By Ben Prince
Sometimes it is a real crap shoot to get the right amount of
coolant in the radiator. At a minimum, the temperature sensor
must be immersed in antifreeze, or otherwise the gauge will
present erroneous readings. Ideally, the fluid level should be
as high as possible to maximize cooling. On the other hand, if
the level is too high, a puddle of coolant will appear on the
garage floor the next time you shut down after a drive on a warm
day.
This "piddling" problem is easily solved with an overflow
bottle. Using a flexible hose and a couple of clamps, the bottle
is readily connected to the overflow tube on the radiator. When
the coolant gets warm and expands, the excess amount flows into
the bottle rather than onto the ground. After the engine is
turned off and the fluid cools and contracts, a vacuum results,
forcing the liquid back into the radiator. With a bottle
installed, one may keep the radiator completely full and not
loose coolant. Most modern cars have this type of system.
Overflow bottles are also often called expansion tanks, surge
tanks, overflow vessels and overflow containers.
The hose from the radiator typically connects at the bottom
of the bottle. The top of the bottle is vented, either with a
small hole or with a vent tube. Normally there is also a capped
opening so that antifreeze may be poured directly into the
bottle.
Overflow bottles come in various shapes and sizes. The
prettiest is a stainless steel cylinder that is sold at hotrod
speed shops. The size that fits the T-cars is about 13 inches
long and 2 inches in diameter, holding a little less than a
quart. It mounts vertically. The one on our TF is attached to
the valence below the bonnet. I made a special holding-bracket
that lines up with existing bolts so that no holes were bored.
Alternatively, I saw a TC at GoF West a couple of years ago where
the overflow cylinder was mounted next to the radiator.
The downside with the stainless cylinder is its $50 expense,
but it does look nice. For a less expensive solution, I once saw
a cylindrical bottle that was made out of PVC irrigation pipe.
Some overflow bottles are shaped approximately like a cube.
The plastic ones sold in discount auto parts stores typically
cost about $6. Another option is use an MGB or Fiat metal
bottle, although they are quite expensive, the MGB one running
about $160.
It is normally recommended that an overflow bottle be
located as high as possible. Frank Travis placed the one on his
TD quite low, however, and he has had no difficulties. I also
saw a picture of a Fiat tank that was located very low between
the dumb irons. It was claimed to operate quite satisfactorily,
so I doubt if high positioning is critical. It is a good idea,
however, to extend the vent tube upward if the bottle is mounted
in a low position.
Another location for the bottle is in the battery box, if
you first install a smaller battery. Although expensive, Optima
brand batteries are a good choice, since they are more compact
than regular batteries, while still providing significant
cranking power. With an Optima battery installed, there should
be adequate adjacent room in your battery holder to install an
overflow bottle.
The radiator cap must be tightly sealed for the overflow
bottle to work. For the pressurized TF, it is also necessary to
install a second rubber gasket in the radiator cap, so that fluid
will flow from the bottle back into the radiator as things cool.
This gasket is 2" o.d., 5/8" i.d. and 1/16" thick. It is
available at most hardware stores.
Later model MGB and Fiat overflow bottles come with
pressurized caps. By installing one of these tanks and its
pressurized cap, and after sealing adequately, you will be able
to convert the TD and TC to a pressurized system. Be careful,
however, to use a low pressure cap (like 4 psi) to avoid blowing
freeze plugs.
I think you will find the overflow bottle a nice addition.
It is relatively inexpensive and is easy to install. The absence
of green antifreeze on the garage floor is a welcome change.
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