Overheat wierdness in Alfetta GTV

[David Rubie <David.Rubie@domain.elided>]

Christmas Eve.  Left work around 4:30pm here in Sydney (fairly hot day, if any
of you have seen footage of the bush fires around the place it might give
you some idea).

Decided to take the "new" tunnel that meets the Airport to avoid traffic lights.
Big, long tunnel.

Anyway, I was pussyfooting around, keeping the car around 2,500 rpm as it had
to do 200+ kilometres down to Canberra from here to meet up with the wife and
kids at their grandmothers house.

About half way through aforementioned tunnel, the temp. gauge starts reading
over 80 degrees C and keeps on going.  Normally, the needle sits dead
between the 8 and the 0, with occasional flicks to either side as the
engine fan kicks in and out.  When the temp. starts to look worrying I
switch out the A/C but it doesn't make much difference.  I also hear
the odd bit of pre-ignition (pinging).  Fearful that I had done something
stupid like leave the oil cap off the engine, or lost a water pump (or belt)
I pulled over as soon as the tunnel finished and started looking around.

Everything looks spot on.  Car did not overheat (i.e. no steam).  I scratch
my head, turn it on without starting it to check the engine fan is working.
Fiddle with the fuses etc.  Nothing out of the ordinary is found.  I didn't
think to check the operation of the engine fan before fuse fiddling, but I
don't know whether it's effective above 40km'h anyway (while the car
was getting hot, I was cruising between 40 and 80, but probably letting
the engine labour a little too much).

I sit there for 10 minutes and take off again, this time driving the bejesus out
of the poor little bugger.  I manage to find a couple of "radar bunnies" on the
way to Canberra and average a, er, bit over the speed limit with no further
problems.  By the end of the trip the car is screaming, running very cool and
faster than I ever remember it (thanks to recent carburettor fiddling).  Used
less fuel too (big surprise).

Has anybody seen this before?  Water pump is newish, belts are good, radiator
hoses are only 12 months old.  Thermostat is 12 months old.  Radiator itself
is of dodgy providence but not leaking obviously, or obviously blocked.  The only
thing I've changed since last summer is a replacement bonnet sound deadening
mat.  I know this is affecting how much heat comes out from under the bonnet
because it no longer makes steam in the rain :-)

Car has tubular extractors, 45mm DHLA carbs, non-standard cams and Crane
XR-700 ignition with timing advanced a little.  Running on 98RON petrol.
I think it has to be either a radiator that is no longer as efficient as it should
be or the car reached some critical temp. point aided by the new sound
deadening mat, but I'm not sure.

Any suggestions?

dave.

1978 Alfetta GTV "trusty" <-- maybe not anymore...
1975 Alfa Spider Veloce "rusty" <-- definitely not any more
1994 Volvo 850 T5 wagon



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