Heater valve

The heater valve is vacuum operated and is used to shut the coolant off from the heater matrix when the heater is set to the cold position and is located here:

The original valve is from a Volvo 740 and probably looked like this when new.

Being metal, it tends to rust through, often from the inside out and can deposit all the coolant spectacularly quickly. This not only occurs in the Elan but most Volvo 740s too and theirs is under the dashboard.

The internals appear to be very restrictive, so this may explain why the heaters in some cars are not very efficient. Fortunately, ScanTech in Sweden make a reasonably priced replacement which is a lot less restrictive and is mostly plastic.

The part number is 51.7896 and these can often be seen on eBay and elsewhere and can range in price from GBP20 to GBP50 or more, however in the UK they can be bought direct from ScanTech's distributer, Braydon Motors who sell them for around GBP10.