John Mates wrote:
List members:
I am thinking a lot about how to plumb my Vanaru transplant. Hobart and
others
are VERY emphatic about the need to move coolant past the thermostat as the
engine warms.
I note, however, in the Subaru engine manuals for my 1994 Legacy 2.2 engine,
that THERE IS ALREADY A BYPASS which runs from the aluminum pipe under
the intake manifold to the heater return pipe. In fact, there are two short
sections
of rubber hose which take the water from a fitting in this pipe to the air
intake and
then back to a short branch off the heater return pipe.
Do I infer that this bypass is insufficient? Was it insufficient in the
Legacy?
On my '90 Urabus and '92 Legacy, it appears the cooling system is plumbed as
follows (Urabus orientation): coolant runs through the engine and out the
large port on the top-left-rear of the motor, then into the top of the
radiator, and out the bottom to the thermostat housing. The heater coolant
runs out the port on the top-right-front of the motor (out of the above
mentioned "aluminum pipe"), through the heater core(s), then back to a pipe an
inch or two away from the output port. This pipe runs down to a point near the
thermostat housing, and a short section of hose completes the circuit returning
the coolant back to the business side of the thermostat. Is your '94
different?
At least one heater valve must be open for hot coolant to make its way to the
sensing side of the thermostat. Or you can, like I did, install a smaller
diameter bypass line from the heater in line to the heater out line (in effect
bypassing both heaters). This way, you can shut both heaters off without
frying the motor.
I'm guessing here, but I imagine the Subaru heater core has a valve which
diverts hot coolant through the core then to the thermostat or bypasses it
directly to the thermostat, depending on the heater setting. Or perhaps
there's always hot coolant flowing through the core and you control heat in the
pass. compartment by opening flaps to control air flow through the core. In
any case you always have coolant flow to the thermostat.
Since I have done the SA 180 degree rotation of the aforementioned pipe, I
will
be able to route the radiator feed directly from the flywheel side of the
engine
forward without having to build the large "L" shaped plumbing required to
bring
the radiator feed forward from near the left rear tail light that others
have built.
The heater end of the rotated pipe will feed the "burp" tank which stays in
its
original position on the rear splashguard. So goes my theory.
Now a question: Can I feed the "burp" tank this way and use the "burp" tank
out pipe (just as was done in the Vanagon) to route more water back to the
heater return to create more bypass flow, if necessary? The reason I want
to
do this is that I imagine that the "burp" tank will capture more bubbles if
water
actually flows through it. A variant of this question is: why is the
"standard"
procedure a routing of the radiator feed water past the burp tank; why not
route
the bypass water past the burp tank, if, as Hobart says, the engine only
sips
from the radiator, but the flow in the bypass circuit must never cease!
Please stop me from cooking my engine if you have reasons to believe this
design won't work!!
It seems to me that you could run the heater outlet into the top of the
expansion tank, then out the bottom to the heaters. This would, as you say aid
in burping air out of the heater circuit. However, I don't know whether this
would aid in burping air from the main coolant circuit. How many bubbles in
the main circuit will take the heater circuit route? With the KEP plumbing,
the expansion tank is on the main coolant circuit and any air that finds its
way past the 'T' to the expansion tank tends to rise and end up in the
expansion tank. With your method, perhaps you could still bleed the system
using the KEP bleeder and elevating the van appropriately.
You could just try it. Watch the dash gauge and/or use the water on cylinder
method (pretty foolproof) to determine if the system is working properly.
Good work!
Dick Myers
'88 Urabus
Grass Valley, CA
