Caveat: I'm used to getting plenty of heat/ defrost at ~50 MPH with the fan off and the heater control ~ 1/2 open. This car has marginal heat with the fan on high.

notes:
- I replaced the thermostat w/ a hotter one and there was a slight improvement.
- The heater core output hose is warm/ hot but I'm not sure my touch-reading of "warm" means much.
- The control works - full open to closed. (I have the kick-panel off.)

It's possible that the core is clogged. I'll look into that later.

Two questions:
1. What fails in the valve eg. does it break inside so that the outside lever works but the inside doesn't? Or does it just clog up? I may pull it today but it looks like tight access to the clamps and messy for the interior.

2. Why does the valve have a thermocouple? I'm used to manual valves that one controls with a cable. Why would you need a thermocouple when your control mechanism is "the car's getting too hot. I'll close the valve some".

There are several threads in the archives about the valve including one from Art B w/ pics and a comment about the adjusting screw "Move the heater control to off (closed) and check that the input hose from the engine to the heater control valve is cold. If not, turn the adjuster screw (arrowed) 3/4 turn clockwise."

Through several 240s I've only had one other with poor heat. The problem is usually too much heat (a non-closing valve I assume).