Richard,
The purpose of the manifold coolant line is to promote
more complete vaporization of fuel, and to avoid
icing, and pooling of liquid fuel in the manifold.
It's an old designer's trick, lot's of motors used
exhaust gas routed through passages in the intake
manifold, the classic 'hot spot' method.
Once the engine and manifolds reach thermal
equilibrium, the coolant is not that much hotter, so
the cost of a thermostat to disable flow through the
manifold was not considered cost effective.
I've routinely left the passage disconnected, but then
again I live in Florida, so cold starting and running
is seldom a concern.
Port fuel injection on modern cars largely eliminates
this concern.
Carter Shore
--- Richard B Gosling <Gosling_Richard_B@perkins.com>
wrote:
>
> Kevin,
>
> The original design had coolant running (from the
> top of the thermostat
> housing) through a conduit in the inlet manifold.
> The idea was to heat the
> incoming air, to reduce the need for the choke.
> This never really made much
> sense to me, as you only need the choke when the
> engine is cold, when the
> manifold heater won't do any heating; once the
> manifold has heated up from
> this coolant conduit, the engine is hot and you
> don't need the choke anyway.
> Moreover, hot air is less dense, so if you suck a
> given amount of hot air into
> your engine you are sucking in fewer molecules, so
> you have less power - this
> is why turbo- and super-charged engines use
> intercoolers, to cool the air
> before it enters the engine. The whole thing seems
> daft to me, but I have
> never got around to seeing what happens if I bypass
> the manifold coolant pipe.
>
> It sounds like your PO has tried what I wanted to
> try (or maybe just broke the
> pipe connectors by accident and decided it was
> easier to bypass than fit a new
> manifold). If your engine runs OK, I would leave
> well alone - unless you are
> concerned with originality, or making it look nice
> and tidy.
>
> Richard & Daffy
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