The factory V8 has three by-pass routes. One is only functional when the
heater valve is open, the second functions all the time, both taking coolant
from the back of the inlet manifold and passing it into the pump, so the
pump circulates coolant through the block, heads and inlet manifold before
the thermostat opens. Thirdly is a small bore hose from the left-hand side
of the inlet manifold to the thermostat cover i.e. it bypasses the stat and
circulates a small volume of coolant through the rad before the stat opens.
It is known as a steam pipe and when it gets blocked you get violent swings
of the temp gauge. After intermittent coolant loss for several years became
constant coolant loss, a top-end overhaul only revealed one problem that I
could see and that was the 2nd bypass pipe referred to above being blocked.
Clearing this and reassembly has removed even the slight fluctuations of the
temp gauge just as the stat first opens, which it had always done and which
I thought was 'normal'. I would have thought an electric pump (as opposed
to a cooling fan) which only came on under the control of a thermostatic
switch was not a good idea, as it would rely on convection, and possibly
conduction to operate during which time certain parts of the cooling circuit
in the engine could be at a much higher temperature than others. Unlike an
electric cooling fan, which generally only cuts in and out at certain times,
I would imagine that once an electric water pump switched on it would remain
on at all times until the engine itself is switched off. Having a
thermostatic switch, apart from possibly allowing wide temperature
differences, introduces a fairly pointless chance of failure, for the
dubious benefits of avoiding the pump running for just the first few moments
after starting the engine. But then, I know nothing about electric water
pumps.
PaulH.
----- Original Message -----
From: "James J." <m1garand@speakeasy.net>
To: "v8" <mgb-v8@autox.team.net>; "buick" <buick-rover-v8@autox.team.net>
Sent: Sunday, January 11, 2004 7:50 AM
Subject: Bypass Tube and electric water pumps
> The little tube that runs from the back side of the water-pump to
> the small tube on the thermostat cover, called the bypass tube: As far
> as I can tell, that allows the pump to circulate a little water through
> the block and heads prior to the thermostat opening. Or is the
> circulation just a way of keeping the pump from cavitating until the
> thermostat opens? Is that correct? If so, is it necessary?
///
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