Re: [alfa] 156 overheating

["Guy Weller" <Guy.Weller@xxxxxxxxxxx>]

Thanks Jonathon, for sharing your analytical logic.

I have
an engine which generates heat
two radiators with fans that dissipate heat
a water filled and pumped transfer system between, controlled by a
thermostatic valve

The water and the thermostatic valve are ok.  The pump certainly circulates
the water, although possibly not as well as it should. It is untested and
remains to me a last resort test because of cost and complexity.
There is one thing that could just indicate poor water circulation.
When it is hot, and I put the heater on full, there is a good blast of hot
air few a few minutes, and then the heat output falls away.  This may just
indicate that the pump isn't circulating water through the rads as well as
it should

I think the discussion over temp sensor(s), guage and idiot light is a red
herring.  I am pretty sure that the car IS overheating, and the the guage
and light are correctly functioning in indicating this.

The radiator is only 4 years old looks clean, has been flushed through (no
sediment) and seems OK.

The fan, or rather the control system, is where I think the fault lies.  The
fan certainly runs.  I hadn't detected two speeds though? And I do think it
is erratic.  On one occasion it came on almost immediately with the car
started from cold. A/c was off and the temp guage hadn't even started to
move and the rad fan came on!

The fan does not run on after the engine is switched off.  Is this correct?
On most other modern cars I  have had the fan continues to run for a few
minutes to dissipate excess heat.  This one just stops as soon as the
ignition is off.

I have found some sort of electrical device mounted behind the rad fan cowl.
I think it may be an air temp sensor.  It has an exposed cylinder the size
of a wine bottle cork with a wire coil which looks corroded and distinctly
unhealthy.

This is currently Prime Suspect, even if it doesn't yet have a name or
obvious function!

Guy

----- Original Message ----- 
From: "Jonathan Coates" <jon@domain.elided>
To: "Alfa Digest (E-mail)" <alfa-digest@domain.elided>
Sent: Wednesday, September 17, 2003 6:37 PM
Subject: [alfa] 156 overheating


> Some thoughts which may or may not help. If the logic is wrong anywhere,
> somebody please point it out.
> The cooling system works by running water araound a circuit using a pump.
> The water gets heated in the engine and cooled in the radiator either/or
> the heater matrix.
> The car shows overheating symptoms when moving slowly / stuck in traffic -
> seems like a low airflow over the radiator takes away less heat - fan
> problem?
> Switching on the heater introduces a second method of cooling the water -
> Temp. goes down - hot comes out of heater - ergo water is going round and
> round.
> Water is also going through radiator as fast moving car does not get hot.
> Seems like the radiator fan is not doing what it should i.e. switch on and
> provide sufficient cooling airflow over the radiator to take away the
heat.
>
> Investigating further - parts CD ( I have no 156 manual) appears to show
> water pump driven off the smooth side of the cam belt.
> I can find no mention of the fan temperature switch on the parts CD so I
> don't know where it is.
> Parts manual does, however, show a resistor on the radiator fan page,
> though no wiring diagram to show what it is for.
> Parts manual also doesnt show (or I can't find) the sender unit. On my 164
> the sender has two terminals so that one does the gauge, the other does
the
> light. dont know which way the 156  does it.
>
> My guess so far is that the problem lies with the fan and is electrical in
> nature. Either the switch is kaput (see below) or the resistor is too
> resisty and is not running the fan on full speed (guessing that the fan is
> a  two speed affair similar to a heater fan). Could also be that the high
> fan speed is not functional.
>
> Possible tests / solutions:-
> IF the fan switch is suspect (and it is) then you can bridge it to make
the
> fan run all day, controlling the engine temperature with the thermostat,
> kind of like driving in very cold weather thsi should do no harm. All my
> cars have a piggy back terminal on one side so that bridging this switch
in
> extremis is easy.
> Bridging the fan resistor could make the low speed turn into high speed,
> though this is not a very good idea as the low speed wiring might not be
up
> to the higher current draw, which will take away the heat more effectively
> showing that the high speed is disabled.
>
>
> Other possibilities:-
> The radiator on the 156 has the supply and return on the same side of the
> radiator. Presumably the radiator header is split internally so that the
> water flows across the radiator and back again. If the baffle is not there
> then the water can short cut the radiator. Does the other end tank get hot
> I wonder?
>
> HTH
> Jonathan Coates
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