From:             "Norm Needham" <Trac4@bigpond.com>
To:               <80_series@sgiblab.sgi.com>
Subject:          Re: [80] Symptom - Overheating
Date sent:        Mon, 22 Nov 1999 09:47:34 +1100
Send reply to:    80_series@sgiblab.sgi.com

From: Clive Myerson <myersonc@one.net.au>

> Norm
> 1) Petrol
> 2) No
> 3) Yes
> 4) Yes & Yes
> 5) Yes
> 6) None Known of
> 7) -
> 8) Been sluggish lately
> 9) Yes
>
> > 1) Petrol or diesel?
> > 2) Could you hear the viscous fan working?
> > 3) AC in use at the time?
> > 4) Was the coolant level OK at the radiator as well as the overflow
> > bottle?
> > 5) Is the engine coming up to normal temperature in normal time from
> > cold start?
> > 6) Any damage to exhaust system?
> > 7) Almost forgot #6
> > 8) Is performance in general normal?
> > 9) Are hoses original?
> >

Thanks Clive,
Now we can make some educated guesses.
1) Just needed to know in relation to other questions.
2) Viscous fan is now first suspect. When the air passing through the
radiator is heated slightly above normal, it causes a spring thingy on
the front of the fan hub to weaken and move. This causes a mechanical
change within the hub and allows the silicone fluid to positively drive
the fan. One should be able to hear the fan roar as it locks up. For a
test, drop a sheet of newspaper down in front of the radiator, run the
engine at about 2,000 rev/min (vehicle stationary). When the temperature
gauge reaches normal or a little above you should hear an obvious change
in fan noise. If there is none, investigate fan further.
3) This may have exacerbated the overheating.
4) Obviously nothing wrong there.
5) Nothing wrong there either. Indicates that thermostat is behaving
normally. There is however a possibility that it is not opening fully.
6) I was thinking more of diesel here. A partially blocked exhaust (lot
of back pressure) can cause overheating. Can happen on petrol but
generally to lesser degree.
7) It's time.  ;-)
8) Might indicate plugs are a bit dicky. Been changed recently? If so,
are they the same heat range as original?
9) Check hoses for "soft" feel. Bottom hose may be sucking closed if
there is any restriction in flow.

There is still other things that could be the problem; like partially
blocked radiator. Aluminium is susceptible to corrosion in core if
proper corrosion inhibitor is not used.
If you have no luck finding the cause, give Peter, Richard, or myself a
ring at work. Advice is free. These things are often better sorted out
on the phone.

Cheers
Norm