A friend dropped up last night in his newly acquired '97 Golf 1.4 - the
interior heater's not working and it occasionally overheats...
So first of all I had a look at the water level - make sure he had some
coolant in it - all was well there...
Next I thought it might be an airlock - so I ran it for a while with the
cap off the expansion tank and massaged the hoses, the hose going into
the heater matrix was very hot - the one coming out not so hot - but
there wasn't a trace of warm air in the cabin...
The radiator was warm so I reckoned the thermostat was ok and hadn't
failed shut, and the fan was cycling on and off...
Then something peculiar happened - when running with the cap off it
would occasionally belch quite a bit of coolant out through the
expansion tank - it would just surge up - and the temp gauge was showing
around 90C at this time.. (the coolant was clean and not discoloured) -
could the head gasket be gone in such a way as to fill the system with a
burst of air now and then? (this happened maybe four times in 5-6minutes)
Is there anything else it could be? - the heater matrix is unlikely to
be clogged it's a relatively new car and the coolant has been changed at
some point... internally maybe it's the baffle or whatever it is that
diverts the air over the heater matrix that has become disconnected from
the control, but as to whats causing it so spit out fluid, I don't know?
In terms of water pump failures - don't they usually just start to leak,
or just seize, it's unlikely to have stopped pumping leading to
localised boiling or is it?
Any advice/theories appreciated,