Volkswagen: VW Polo internal heater, engine thermostat, coolant lines

Question
Thanks Ron. Great prompt response. I won't have time to do any of this work for a few days but I need the car! Is there a danger the engine may over heat because the core and thermostat are plugged? Or is the system independent of the engine cooling circuit?


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Followup To
Question -
I have a 1995 VW Polo (Ireland). The internal heater has stopped working. The fan still works fine, but there is just no heat control. I do not have A/C. The engine temperature seems fine and the coolant level is OK.

Do you think there's something wrong with the thermostat - is it the same thermostat as for the rest of the engine? If so, if it is damaged is the car in danger of over heating? Is the engine thermostat under the top radiator hose and just beside the engine block?

Could it be something else? Could it be something in the console of the car away from the engine?
Answer -
Hi Will,

The most common cause of a problem like this: the heater core is plugged up.

The first thing you should do is replace the thermostat, it is inexpensive, and if the heater core is plugged, the thermostat is likely to be cruddy as well.


Next, find where the two coolant lines connect to the heater core (on the firewall, left side as you are looking into the engine.   Make sure the engine is completely COOL. (after sitting overnight)

Disconnect the two lines, and see if you can pass water through it with a garden hose or similar.  If you cannot, you know the problem is with the heater core.

There are two ways to diagnose the rest of this:

1) Look under the dashboard and see where the "Hot" switch for the heat connects to the box around the heater core.   Have someone move the switch back and forth, make sure it is moving freely.

2) If you cannot get water to pass out of it freely, you will probably have to replace the core.

If that is the case, a professional VW shop should perform this, or you can get an Official VW Service Manual and perform the job yourself.

Please let me know how you make out.


Ron

Answer
You should have no trouble as long as the needle for the temperature is moving, and staying in the 'normal' range.

Only if the temp gage tends to stay at 'cold',  that generally means the thermostat is stuck closed, and needs to be replaced right away.

If the heater core is plugged,  the water just bypasses it.

Sounds like you diagnosed it pretty well, so, no worries at all,  you will be fine.