Re: Boiling Guilia Super

[Scott Fisher <sfisher71@domain.elided>]

--- Timothy Leigh Rodgers <timothy@domain.elided>
wrote:
> Driving from Santa Barbara up San Marcos Pass-

I know it well.  GREAT sports-car road.

> [...] I noted that the upper and lower
> radiator hoses were collapsed.  I waited for the 
> engine to cool and removed the radiator cap.
> Immediately the hoses reexpanded.  I added about two
> quarts of water, and the car drove fine [...] No
more
> overheating, no collapsed hoses, no loss of coolant.
> I'd appreciate any ideas as to what happened and
> why, and what I can do to
> prevent such problems in the future.
> Thanks in advance for your assistance.
> Timothy
> '71 Alfa Romeo Giulia 1300 Super

First, some theory:

Engine heat makes coolant expand.  While pressurizing
the cooling system is important to its function
(because higher-pressure systems can absorb more
heat), the increased volume of coolant has to go
somewhere -- preferably before it goes out the head
gasket or a split in the hose.  In my '67 GT Junior,
it went out through a rubber hose mounted to the
radiator filler neck and dumped onto the ground just
to the side of the radiator.  In my '74 Spider, it
goes out a rubber tube in the same location, but is
captured in an overflow tank mounted just inboard of
the, er, LEFT front wheel (there, Joe, I got the left
right this time, or is that the right left?).  In my
Berlina, it goes out a crack where the header tank is
brazed/soldered/stuck to the radiator core, but that's
because I haven't fixed it yet.

The EXACT answer in your Giulia Super most likely
depends on whether your '71 is like my '67 or like my
'74.  (Or, in a worst-case scenario, on what your head
gasket is like.)

In any of these cars (except my Berlina with the
crack), the principle is that hot coolant expands;
when it reaches a certain pressure, the spring in the
radiator cap relaxes and coolant flows out the
overflow tube in the radiator neck.  Then, what
happens depends on the year of the car -- and I don't
know what your '71 is like.

In the '74 cars, the coolant goes into the overflow
tank.  When the system cools down, the pressure inside
the cooling system is lower than ambient, and the
coolant gets sucked back into the radiator.  Virtually
all modern cars work this way because it reduces the
amount of attention the driver has to pay to anything
other than the cell phone, the GPS, and the climate
control system.  Evaporative coolant loss is minimal,
and a car with an overflow tank may take coolant once
a year.

In my '67, though, the coolant ran down the overflow
tube and out of the car -- this is sometimes referred
to as a total-loss cooling system.  This reduced the
amount of coolant in the system, which put more load
on it, which made it expand more, which made it flow
out, which reduced the amount of coolant, which put
more load on it, which -- you get the picture:
self-accelerating thermal runaway.  Now, don't think
I'm dissing Alfa: pretty much all the Sixties-era cars
I've owned (with the notable exception of the 356, of
course) were designed this way, because it was
expected that car owners -- or gas-station attendants
-- would add coolant as required.  The system works
fine as long as you keep it topped up.

So, Timothy, somewhere in your drive up San Marcos
Pass, your engine started using coolant, which made
the residual coolant hotter, which used coolant
faster, which made the residual coolant hotter, etc. 
The question is, where did it go, and why didn't the
system equalize pressure (with coolant, if it's got an
overflow tank, and with air, if it's a total-loss
system) after it cooled off?

That's part of what suggests my worst-case scenario:
that instead of going out the overflow tube, your
coolant is going into one of your cylinders via a
head-gasket leak.  It's just one possibility, but it's
one to investigate and, with luck, eliminate.  (A
head-gasket leak would also explain the loss of power
as you were climbing the grade.)  I'd start with a
compression test on a hot engine (in case the leak
only shows up when something expands), and in
particular look for one cylinder a lot lower than the
others.  I'd also look for rust on the spark plug
threads in one cylinder when I took them out prior to
the compression test.  If your pressure readings are
something like 150-150-150-85 and the spark plug from
the 85-psi cylinder is rusty, I'd start shopping for
head gasket kits.

But don't yank the head just yet.  It could be
something as simple as a faulty radiator cap that is
allowing pressure to ESCAPE but not letting anything
(air or coolant) back in.  You used to be able to have
radiator caps tested; today it's probably a lot
cheaper just to buy a new cap with the right rating.

If your '71 has a coolant overflow tank, you should
also look to see whether there is any liquid IN the
tank, and if not, replace the rubber hose from the
radiator to the bottom of the tank.  They do split
over time, and I have resolved at least one puzzling
cooling-system problem (on a non-Alfa) by replacing
the rubber hose (with an all but invisible crack) to
the overflow tank.  You might also remove the tank,
clean and degrease it (spoken like a true 2-liter
owner!), and make sure it has no cracks or leaks
itself.  It's possible that a crack in the overflow
tank could leak when the pressure inside rises, but
NOT when internal pressure is less than ambient
(pressure from within expands a circle, pressure from
without compresses it and seals the leak).

And thinking of that -- of a flexible leak which
allows pressurized gas/liquid to ESCAPE but which
seals when internal pressure is less than external --
you might also check your heater hoses and other
cooling system passages.  Again, it's barely possible
that you could have a leak OUT of a hose where it
meets the metal fitting on the engine, but when the
pressure shifts, the suction pulls the rubber hose
TIGHTER onto the metal fitting.  It's a stretch (no
pun intended), but this is what I mean when I talk
about pre-emptive maintenance.  Preventive maintenance
is flushing the cooling system and keeping it topped
up; pre-emptive maintenance is changing ALL the hoses
when one splits.  (And OBSESSIVE pre-emptive
maintenance is changing all the hoses on your Alfa
when one hose splits on your Audi. Did that two years
ago... but neither car has cooling problems today. :-)

--Scott Fisher
  Tualatin, Oregon
.
Yahoo! - Official partner of 2002 FIFA World Cup
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